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Welcome to the eighth edition of the Atkins Technical Journal which featurespapers covering design, strategic advice, research and thought leadership acrossa broad range of disciplines. All the papers showcase the innovation we bring,

whether through improving composite aerofoil design, producing a concept for a3D interchange viewer and walk planner, or developing a mobile system to managehighway defects which has enabled a 52% cost and efficiency saving. Coupled with

this, however, remains a strong focus on technical governance and data security;systems engineering approaches feature strongly throughout.

The success behind much of the work described can be attributed foremost tothe high calibre of our teams, but also to their adherence to sound principles fortechnical delivery. It is evident that the teams featured had an excellent grasp andunderstanding of our client’s requirements at the start of the project and then

delivered on time and to budget through effective project controls, checking andreview. Many of the key lessons learnt have been captured for re-use through thepapers in this Journal. It is no coincidence that precisely these behaviours are beingreinforced through the recent introduction of Atkins’ global Design Principles.

I hope you enjoy the selection of technical papers included in this edition. This eighthJournal, and all previous editions, are available on our external website. We areintroducing an email subscription alert service for future editions. To find out more,

please visit:

www.atkinsglobal.com/en/about-us/our-publications/technical-journals

Chris HendyNetwork Chair for Bridge Engineering

Chair of H&T Technical Leaders’ Group

Atkins

F or e w or d


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C on t e n t s

Cyber Security

120 Cyber security and critical national infrastructure Environment 121 Modern technique for leakage detection at dams 122 Roman snail: An introduction to its ecology and legal protection 123 Gainsborough flood alleviation scheme: Improving project delivery through an

integrated team approach to reusing existing assets 124 Lake water budget modeling white paper

Rail

125 Orient Way carriage sidings: Design and Construction

Structural Dynamics

126 Structural analysis of composite aerofoils using aero - and inertial - elastic tailoring 127 Management’s responsibility for lively structures

Structures

128 Design of Aberdeen Channel Bridge, Hong Kong 129 Bearing replacement and strengthening of Forth Road Bridge approach viaducts, UK 130 Design of cross-girders and slabs in ladder deck bridges

Systems Engineering 131 Resolving complexity: Why system engineering works 132 Somerset Highways’ mobile highways management solution 133 Industrial innovation management: A systems approach 134 3D interchange viewer and walk planner

Technical Journal 8Papers 120 - 134

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C y b e r S e c ur i t y

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Why cyber security is important for national

infrastructureICS and SCADA are utilisedthroughout national infrastructurein water, electricity, gas, petroleum,pipelines and transport. They areubiquitous in manufacturing andeven drive diverse things such astheme park rides, baggage systemsand ski lifts.

As it has developed, cyberspacehas enabled the automation and

optimisation of the infrastructurethat supports many businesses;for example, the SCADA systemsthat automatically control andregulate industrial processes such asmanufacturing, water distribution,refining and power generation. – UKCyber Security Strategy, Nov 2011

ICS and SCADA are the buildingblocks of automated systemswhere control or monitoring of aprocess is required; many also have

varying degrees of safety-relatedfunctionality, from protectingoperators, users or customers tomembers of the public. The potentialdisruption from a cyber event couldbe significant and not just in terms

of loss of revenue, reputation anddamage to affected brands. Forexample, 80% of the UK populationrely on five supermarket retailers whohold only four days’ worth of stockin their supply chain, so a cyber eventcould have a far reaching impact.(Defra 2006)1.

The scale of the challenge

Two recent publications in the UKhave underlined the importanceof protecting critical nationalinfrastructure and the scale of thechallenge.

The UK Parliamentary Office forScience and Technology (POST), abody that provides independentanalysis of policy issues with ascience and technology basis,published a briefing entitled ‘CyberSecurity in the UK’2. The briefing

highlighted recent events in cybersecurity and discussed the potentialfor large-scale attacks on nationalinfrastructure, related emergingissues and the implementationof cyber security. Topics coveredincluded responsibility for UK cyber

Cyber security and criticalnational infrastructure

Abstract

Cyber security is an all-embracing term, meaning different things to differentpeople, but fundamentally it is the defences which shield computer systemsfrom electronic attack. These may range from relatively small-scale emailscams through to state-sponsored disruption of computer-based systemsthat run critical national infrastructure, such as the electricity grid, water or

transport networks.Governments and organisations that manage national infrastructure,therefore, face a challenge to ensure their systems are adequately protected.Moreover, the steps they put in place must protect from a range of cyberthreats that are constantly evolving.

This paper explores the challenges faced by organisations and the standardsand approaches which can be applied to help protect their systems, inparticular Industrial control systems (ICS) and Superviisory control and dataacquisition systems (SCADA) systems.


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that Microsoft Windows parses TrueType fonts and when successful, itprovides a tunnel enabling nefarious

running of arbitrary code with fullsystem privileges. This might includeinstalling application, viewing,changing, deleting data and creatingnew administrator accounts. Duquoperates on virtually all supportedversions of the Windows operatingsystem.

Microsoft subsequently offered atemporary workaround and laterreleased an official operating systempatch. Research by Microsoft, in

preparation of the patch, alsohighlighted the potential underlyingvulnerability to be exploited bybrowser based attacks, referring toInternet Explorer, but this could alsoextend to other browsers.

on industrial control systems anddiscovering vulnerabilities forsubsequent analysis and exploit

development. It is not destructive,unlike Stuxnet, instead it stealsinformation, including interceptingkey strokes and taking screen shotsand hiding the data in jpeg typeimages (Figure 2). The stolen datais then encrypted and transmitted viaseveral compromised servers to maketracking more difficult. After 36 daysthe Remote Access Trojan removesitself, providing a high degree ofstealth and making identification

of affected systems difficult. In atleast one instance Duqu installed,via a previously unknown kernelvulnerability exploit targeted viaMicrosoft Word documents.

Duqu exploits a flaw in the way

security, types of attacks and anemphasis upon industrial controlsystems and the need to improveresilience, security and knowledgein both industry and Government.The POSTnote highlighted that 50%of respondents in a recent survey ofsecurity specialists across the industrystated there was a case for improvingtheir cyber defences.

This was followed by the UKGovernment’s Cyber Security

Strategy3

, which outlines aprogramme of Government activityto work closely with companiesresponsible for critical nationalinfrastructure systems. Moreover,it announces the Government’sintention to work with a widerrange of companies than thosecurrently associated with nationalinfrastructure; anywhere where thethreat to revenues and intellectualproperty is capable of causingsignificant economic damage is nowfirmly on the Government’s radar.

Nearly two-thirds of criticalinfrastructure companies reportregularly finding malware designedto sabotage their systems. McAfee,Critical infrastructure protectionreport, March 2011.

Malware that targetscontrol systems

In the same period as thesepublications, the antivirus firmSymantec released details of a newTrojan called ‘Duqu’, originallythought to be aimed at industrialcontrol equipment vendors. Duqugives an indication of the type andcomplexity of cyber threats that faceorganisations which manage criticalnational infrastructure.

Symantec has hailed Duqu as theprecursor to the next ‘Stuxnet’, aprevious worm that targeted physicalinfrastructure (and is believed tohave been designed to target Iraniannuclear systems). Duqu functionalityshows it is the foremost intelligencemechanism for gathering information

Figure 1. Stuxnet infection routes


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Duqu was almost certainly writtenin Object Oriented C and compiledin Microsoft Visual Studio 2008,according to research undertaken byKaspersky Lab. Why would this besignificant? It indicates professionalprogramming techniques usedby ‘older’, more experiencedprogrammers employed on softwareprojects. Whoever they are, theyremain active, in March 2012 a newelement of Duqu was discovered.The new Duqu driver was designedto avoid detection by antivirus toolsdeveloped by the very same groupof researchers in Hungary, whooriginally discovered the Duqu Trojan.

Early versions of Stuxnet had similarfunctionality to Duqu (Figure 1);fingerprinting configurations ofindustrial control systems whichwere then attacked in a very precisemanner, whilst infected non-matching configurations remainedphysically unaffected. The similarityalso extends to the use of identicalsource code, indicating that theperpetrators are likely to be thesame skilled and highly resourcedgroup responsible for Stuxnet. Bothmalwares provide blueprints forfuture attacks, although the highlevel of sophistication limits thenumber of entities with the resourcesavailable to launch such attacks.

Ever wondered how malware isnamed? Some files created by theDuqu Trojan begin with the lettersDQ. This is a variant of the Stuxnetworm which is believed to have beentargeted at Iran’s nuclear programmewith the aim of disrupting processingby making changes to industrialcontrol systems. This was a definingmoment; Stuxnet was the first virusto target physical infrastructure, asopposed to abstract IT systems. Duquis both very similar and yet different,instead of the payload that targets

control systems, Duqu’s payloadcontains the means to reconnoitrenetworks and steal information.

Figure 2. Data is encrypted in a JPEG file of a Hubble image of NGC6745

Stuxnet: An unusually complex threat

Stuxnet has been described by Symantec as one of the most complex threatsit has analysed, including:

• four zero day exploits (those exploits that are unknown, undisclosed tothe software vendor, or for which no security fix is available – a rarity forany virus that would be considered wasteful by most hackers);

• Windows rootkit – software that enables privileged access to a computer

whilst hiding its presence;

• first ever ‘PLC rootkit’ – infecting PLC programs and remainingundetectable;

• antivirus evasion;

• two stolen Taiwanese digital signatures;

• complex process injection and hooking code (to prevent programmersseeing the infected code);

• network infection routines;

• privilege escalation;

• peer-to-peer updates;

• remote command and control.

Box 1. An outline of Stuxnet characteristics


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understanding of cyberspace andhow it is developing. – UK CyberSecurity Strategy, Nov 2011

In the majority of cases compliancewith ISO standards for informationassurance is voluntary and thisis widely seen as beneficial. Theabsence of regulation in industrialcyber security ensures thatdevelopments in this fast-movingarea are not stifled. However this alsomeans that cyber security for critical

national infrastructure is far from asimple checklist exercise.

Organisations wishing to protect theirICS and SCADA must keep abreastof technical developments and put inplace systems that balance adequateprotection with flexibility. The keyis to adopt an holistic approach toimplementing a range of measuresthat provide defence in depth,whilst recognising that cyber securityis a continuous process and that

contingency planning for inevitablecyber events is crucial.

How is Atkinsadvancing cybersecurity?

Atkins are leading innovations incyber security, an example is thedevelopment of new sector specificstandards for securing industrial

control systems and SCADA. Thegoal is to improve systems resilienceby education and raising awarenessof the need to protect systems whereit is often difficult to articulate thesecurity requirement and thereforechallenging to obtain investmentagainst other more tangible businesspriorities. Since the approaches toICS security differ from informationassurance, with an emphasisupon different business goals, thenew standards provide a basis for

applying proven methodologiesand techniques to this specific area.Ongoing work is addressing thegaps the Information AssuranceFramework (ISO 27000 series) andwill provide a scheme for common

foolproof as vulnerabilities andweaknesses could be identifiedat any point in time. In order toreduce these risks, implementingmultiple protection measuresin series avoids single points offailure.

3. Technical, procedural andmanagerial protection measures– Technology is insufficient on itsown to provide robust protection.

Additional specific technical

standards are in preparation andwill form the basis for European andinternational approaches to industrialcyber security. Work currently takingplace in IEC (preparing the IEC62443 standard) is incorporatinga management framework thatembodies the approach of theISO 27000 series familiar to the ITindustry, addressing the gap in thewidely adopted IT managementstandard.

Further technical and managementstandards that will form a frameworkfor UK implementation of industrialcyber security, include the workdone by the US International Societyof Automation (ISA). The ISA haspublished the ISA-99 series ofstandards that deals with IndustrialAutomation and Control SystemsSecurity and collaboration betweenISA and IEC is developing a similarseries of technical standards under

IEC 62443 which will incorporatea management framework thatembodies the approach of the ISO/ IEC 27000 series.

Protecting against cyber attacksrequires action at many levels.Implementing technological solutionsis vital but the skills, behaviour andattitudes of personnel are equallycrucial – POSTnote, September 2011

Defence in depthcoupled with agility

The pace of technological changeis relentless. Keeping pace willrequire people who have a deep

Protecting against cybersecurity threats

Against this backdrop, how doorganisations protect critical nationalinfrastructure from cyber threat?

Organisations generally manageinformation risk using InformationAssurance (IA) processes based onISO/IEC 27001 and ISO/IEC 27002standards that were originally

developed in the UK.

These series standards are a risk-based management system thatspecifies the overarching structuralrequirements for informationmanagement frameworks. Assuch, they are flexible dependingon the requirements of the specificorganisation in question and do notrequire specific security measures tobe implemented.

Rather than focusing on specificattack examples when designingsecurity measures, it is consideredbest practice to use an holisticapproach employing a combinationof solutions to address a widerange of possible vulnerabilities. –POSTnote, September 2011

For more specific technicalguidance on ICS and SCADAsecurity, organisations can considera number of sources. In the UK,

the Centre for the Protection ofNational Infrastructure (CPNI) is theGovernment authority that providessecurity advice to the nationalinfrastructure. Specific SCADA adviceis offered by the CPNI in a series ofprocess control and SCADA securitygood practice guidelines, whichhave three guiding principles at theirheart:

1. Protect, detect and respond– It is important to be able to

detect possible attacks andrespond in an appropriatemanner in order to minimisethe impacts.

2. Defence in depth – No singlesecurity measure itself is


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programme management thatincorporate appropriate measuresfor SCADA and industrial controlsystems.

Potential industrial control systemsincidents 4

• blocked or delayed flow ofinformation through ICSnetworks, which could disruptICS operation;

• unauthorised changes to

instructions, commands oralarm thresholds, whichcould damage, disable orshut down equipment, createenvironmental impacts, and/orendanger human life;

• inaccurate information sentto system operators, either todisguise unauthorised changesor to cause the operators toinitiate inappropriate actions,which could have various

negative effects;

• ICS software or configurationsettings modified or ICSsoftware infected withmalware, which could havevarious negative effects:

• interference with the operationof safety systems, which couldendanger life.

Box 2. Potential impacts of ICS incidents

References

1. Defra Groceries Report 2006 http://archive.defra.gov.uk/evidence/economics/foodfarm/reports/documents/Groceries%20paper%20May%202006.pdf

2. POSTnote 389, September 2011.

3. UK Cyber Security Strategy, Cabinet Office, November 2011

4. National Institute for Standards and Technology Special Publication80-82, Guide to Industrial Control Systems (ICS) Security, June 2011


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Introduction

Many dams leak and unless itincreases in quantity or starts totake materials with the flow, it is notnecessarily a problem. However, ifsome sort of erosion process takesplace and the flow increases, thenfailure could occur. Remedial workswould normally involve comparativelyexpensive techniques of grouting orslurry trench valley etc., but if theextent and location of leakages canbe accurately predicted the amountof remedial works and so costs canbe limited.

This paper describes the techniqueand how it was used to locateleakage and the proposed remedialworks at a 200m high rockfill dam inSri Lanka.

The WillowstickTechnique

Controlled Source – Audio FrequencyDomain Magnetics (CS-AFDM),nicknamed Willowstick, is ageophysical technique that usesa low-voltage, low-current audiofrequency electrical signal to energise

groundwater or seepage flows in theareas of interest. The Willowstickmethod works by measuring thesignature magnetic field responseof a controlled, alternating electriccurrent (AC) flowing through a

specifically targeted subsurface studyarea – ie the dam and its foundation.

The Willowstick magnetic field iscreated by a large electric circuitconsisting of three parts: (1) the

antenna wire connecting two ormore electrodes; (2) the electrodesor points of coupling with the earthand (3) the targeted subsurface studyarea itself, which is located betweenand/or around the strategicallyplaced electrodes. The diversityof site conditions in dams oftennecessitates wide variations ofelectrode and antenna configurationsand interpretive parameters.

For a leaking dam, electrodes are

placed upstream and downstreamof the embankment or structure.The upstream electrode is placedin the reservoir water at sufficientdistance from the dam to allowelectric current to spread out in thereservoir before reaching the faceof the structure. The downstreamelectrode is placed in strategiclocations (seepages, observationwells or other downstream locations)to facilitate contact with seepage

flowing through the dam. Theelectrical current follows preferentialpathways by concentrating in zoneswithin the saturated subsurface thatoffer the least resistance through,beneath, and/or around the dam’sstructure. As the electrical current

Modern technique for leakagedetection at dams

Abstract

This paper describes a technique called Controlled Source Audio FrequencyDomain Magnetics to track, map and monitor leakage through dams.

The problem most dam engineers face is that leakage can often be tracedat the toe of a dam or downstream of it, in some cases upstream within thereservoir basin, but it is usually very difficult to track the leakage through or

under the dam.

The ‘Willowstick’ technique, described in this paper, allows individual leakagepatterns to be mapped through or under dams.


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algorithms, measures the strengthof the signature magnetic field andconverts all the information into

a recordable data set that is readyfor subsequent processing andcorrections (collectively called datareduction).

Physical Principles involved inWillowstick

The following principles used byWillowstick show how the techniquecan be applied to identify, map andmodel electric current flow pathsthat infer groundwater distribution

patterns through the subsurface:

• Electric current follows the pathof least resistance. Groundwateris generally the best subsurfaceelectrical conductor.

• Electrical current flowing in aconductor generates a magneticfield with characteristics thatreflect the location of its source.

• Based on Maxwell’s equations,an alternating electrical current

in a conductor will generate analternating magnetic field aroundthe conductor. The converseis also true. An alternatingmagnetic field will generate analternating electrical current in

groundwater of interest, while at thesame time optimising funds availablefor the investigation.

Each measurement station’s X, Y,and Z coordinates are recorded aspart of the field work. The stationsare designated by small red crossesor “+” signs shown in the figures.These spatial locations are criticalto data processing, comparison ofsurveys, modelling and interpretation.

Equipment

The equipment used to measure themagnetic field induced by electricalcurrent flowing in the groundwaterof interest includes: three magneticsensors oriented in orthogonaldirections (X, Y, and Z axis); a datalogger used to collect, filter andprocess the sensor data; a GPS usedto spatially define the field locations;and a Windows-based handheldcomputer used to couple the GPSdata with the magnetic field dataand store it for subsequent reductionand interpretation. All of this

equipment is attached to a surveyor’spole and hand carried to each fieldstation (see Figure 2).

The Willowstick, filters and monitorsvarious frequencies, amplifies thesignals through noise-reduction

takes various preferential flow pathsthrough, beneath, and/or aroundthe dam, it generates a magneticfield characteristic of the electricalcurrent. This unique magnetic fieldis identified and surveyed at theground’s surface in a grid patternusing sensitive magnetic sensors.

The horizontal and vertical magneticfield magnitudes are measured ateach grid measurement stationon the surface of the ground

to define the electrical current’ssubsurface distribution and flowpatterns. In nearly all cases,the paths of least resistance forelectrical current to follow inferzones of higher porosity within thesaturated subsurface. The locations(coordinates) of measurementstations are obtained using a GlobalPositioning System (GPS) unit andare recorded in a data logger alongwith the magnetic field data. Themeasured magnetic data are thenprocessed, contoured, modelledand interpreted in conjunction withexisting hydrogeologic informationto enhance the characterisation ofgroundwater beneath the area ofinvestigation.

The overall approach to thefieldwork involves energising thegroundwater of interest withan AC electrical current with aspecific signature frequency (380

or 400 hertz) between the pairedelectrodes. As the electricalcurrent follows preferential flowpaths in the study area betweenthe electrodes, it generates arecognisable magnetic field thatis measured by sensitive coils.Magnetic field measurements aregenerally taken along lines rangingfrom 5 to 15m apart with stationson each line spaced at 5 to 15mintervals. These distances vary fromone project to another depending

upon resolution requirements andother site conditions. The gridpattern proposed for any particularinvestigation is designed to providesufficient detail and resolutionto adequately delineate the

Figure 1. Typical Horizontal Dipole (Plan View)


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communication cables,overhead and undergroundpower lines, undergroundmetallic pipelines, metal fences(chain link, barb wire, etc.),railway tracks, steel guardrailsand other elongated continuousconductors. The locations ofsuch are usually known, thusthey can be accounted for wheninterpreting the data.

3. The third class of conductor

is wet clays, which oftenpose a problem in DCresistivity and other electricalor electronmagnetic (EM)methods. Near surface clayscan act as a “shield” and causemuch difficulty measuring theelectrical properties of materialsbeneath. The Willowstickmethod has two advantages:Firstly, it measures the magneticfield response which is notdirectly affected by wet claysas are the electric field or EMfield. Secondly, by directlyenergising the medium ofinterest, greater control can bemaintained in most cases tominimise the amount of electriccurrent straying and flowing inthe wet clays. In most cases,natural subsurface watersmoving through a channel willhave a lower resistivity thaneven wet clays, so the current

will tend to focus in these if theproper energising perspective isemployed.

4. The fourth class of conductorto consider is any and all othergeologic semi-conductorssuch as graphite-bearingshale, sulphide ores and ironformations. Because of theirnature and distribution, thesegeologic materials are rarelypresent in significant quantities

to cause a problem aroundWillowstick surveys.

Interpretation and Modelling

After data reduction is complete, oneor more footprint maps are created

of the magnetic field emanatingfrom the primary coil.

• Conductive features will gatherelectrical current flowing in theground. This is referred to ascurrent gathering. Electric currentflowing in the ground will followlong conductors or conductivezones that facilitate conductionbetween point A and point B (i.e.

the two electrodes). The longsubsurface conductors or semi-conductors can be formed intofour general categories:

1. The first class of conductors issubsurface groundwater flowpaths and channels. Whenelectric current is biased to flowthrough a subsurface studyarea, the electrical current willtend to concentrate and flow inthe most conductive medium,

which is the groundwater/ seepage/leakage.

2. The second class of conductorsis ‘culture’, or any longcontinuous conductor that isman-made. These include:

a conductor that is under theinfluence of the alternatingmagnetic field.

• Two coils in close proximityto each other can be coupledmagnetically. A transformer is aspecial case of two magneticallycoupled coils. The electriccurrent in the primary coil createsa magnetic field which then

induces an electric current inthe secondary coil, completingthe magnetic coupling. Theprimary coil in the Willowsticktechnology is created by a largeprimary loop that consists ofthe antenna wire, electrodesand the preferential conductivepathways (groundwater) inthe subsurface between theelectrodes. The Willowsticktechnology’s secondary coils are

in the magnetic receiver. Whenthe magnetic receiver is underthe influence of the magneticfield emanating from the primarycoil (conductive subsurface flowpath), the three receiver coilssense and measure the strength

Figure 2. Willowstick Instrument


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is generally determined with a highdegree of consistency and accuracy.

The results obtained from aWillowstick geophysical investigationare used to make informativedecisions concerning how to furtherconfirm, monitor and possiblyremediate groundwater problemsthrough a given area of investigation.

Example of the

Willowstick System inpractice

The Dam is located in Sri Lanka just off the southern tip of India.The dam is located approximately160km southeast of the capital city,Colombo (see Figure 4).

The Samanalawewa Dam impoundsthe Walawe River, the fifth largestriver in Sri Lanka. The Walawe Riverin conjunction with another major

tributary - the Belihul Oya River -flows from the mountains of centralSri Lanka. The two rivers flow inparallel valleys in a southeasterndirection and eventually jointogether. The horizontal separationof the two rivers is roughly 6km,while the vertical separation betweenthe Walawe River (after joining theBelihul Oya River) and Katupath Oya(a tributary of the Walawe) is over300m. This difference is used as the

head for Power Generation.The construction of theSamanalawewa Dam was startedin 1986 and completed in 1991.The dam and resultant reservoir areone of the largest storage facilitiescreated in recent times in SriLanka. The dam is a zoned rockfillembankment with clay core, roughly105m high and 530m long andretains a reservoir with a capacityof 254mm3. The catchment area

of the dam covers nearly 350km2

.Not only is the dam important forits renewable energy resource,but it also serves as a key elementfor water supply, flood control,fish and wildlife and many other

one electrode to the other inorder to complete a circuit. Thevariable part of the circuit - andthe interesting part - is whathappens to the electric currentwhen it is allowed to chooseits own paths to flow betweenelectrodes. It is always true,however, that 100% of theelectric current must concentratein and out of the points ofcoupling (the electrodes), andhence the magnetic field tends togrow much stronger as it nearsthese points.

Interpreting magnetic field contourmaps could be compared to readinga topographic quadrangle map.On a topographic map, the ridgelines connecting the peaks could bethought of as the pathways offeringthe least resistance to traverse. Inthe same way, these lines in themagnetic field maps represent pathsof least resistance for electricalcurrent to follow, although itundergoes some measure of dispersaland regrouping in more complexways than can be fully described. Byidentifying these high points andridges and connecting them togetherthrough the study area, the centreposition of strong preferential electriccurrent flow can be identified (seedark blue lines in Figure 3). Notethat the flow paths attributed toculture are highlighted to keep them

separate from those attributed togroundwater.

In some cases electric currentflow paths produce very tight andrevealing anomalies that can bemodelled with a fairly high degreeof accuracy (depths to within 10%error). Other times electric currentflow patterns are not as distinctiveand the depth and character canonly be roughly estimated—in whichcase it is very important to have

additional data to help characterisethe groundwater zone of interestsuch as, well logs, piezometric dataor other geophysical or hydrologicaldata. In any case, the horizontalposition of electric current flow paths

to reveal the patterns of electricalcurrent flow in the subsurface byshowing contrast between areas ofhigh and low electrical conductance.

When identifying anomalouspatterns in a typical footprintmap, it is important to be able todistinguish the three main influenceson electric current flow. Besides thegroundwater influence, the residualeffects of culture and electric currentbias still exist in most cases - even

though the data reduction processesmay have reduced these effects tosome degree. These three maininfluences are discussed below:

1. The groundwater influence in atypical footprint map is obviouslyof greatest importance. Asdiscussed, Willowstick is basedon the principle that its signatureelectric current is stronglyinfluenced by the presence ofgroundwater, or areas of higher

porosity where groundwater isaccumulating and/or flowing.The electrical current will naturallygather and concentrate in theseareas or pathways of higherconductivity, which are revealed inthe footprint map.

2. The magnetic field may beinfluenced by culture, whichis any conductive man-madefeature such as pipelines, powerlines or other long continuous

conductors. Culture is notalways present, but it is oftena factor and sometimes veryproblematic because it tends tobe near-surface and can causelarge anomalies that mask someof the signal coming from thesubsurface. The best approachis to identify all culture beforea survey is initiated and eitheravoid as much of it as possible bystrategic survey design or remove

its effects when interpreting thedata.

3. The magnetic field in any givensurvey is always subject toelectrical current bias becauseelectric current must travel from


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by 1,600m-long grout curtain was

constructed.

‘Leakage incident’ andsubsequent remediation

On 22nd October 1992, water burstout of an area downstream of theright abutment of the embankmentwhen the water had reached a levelof 439.01m OD. The water levelwas immediately lowered to 430mAOD over a period of three weeksending on 11th November 1992.However, groundwater levels inthe right abutment area were kepthigh as a result of a blockage at thedownstream end of the ‘karst/pipefeature’. Once this blockage hadbeen removed the groundwater leveldropped by 2-3m in the abutmentarea. Nearly 25000m3 of earth werewashed away from the adjacenthillside.

The next remediation effort consistedof installing a dumping of clayfrom barges in an attempt to slowseepage flowing out of the reservoirinto suspected ingress areas alongthe noted fault zones. However,after installing nearly 50,000m3 of

a number of minor, parallel faults

which create the saddle featuresnoted above. This and other signsof possible leakage through theright abutment area resulted in anextensive grouting program. Sixlarge cavities, similar to that shownabove, were found and sealed withconcrete during construction.

Measures to limit waterlosses

During the construction of the damfour adits were driven along the axisof the dam.

Despite efforts to cut off seepagethrough the right abutment area, asmall spring appeared downstreamof the dam upon initial filling of thereservoir (June 1991). The seepagewas large enough to suspend fillingthe reservoir. Additionally, a flatwater table was observed respondingto the reservoir levels up to a distanceof 2.5km from the dam (along thereservoir’s right rim). As a remedialmeasure, a 1,880m long tunnel wasdrilled beneath the right rim area.From inside the tunnel, a 100m deep

immeasurable benefits to the countryof Sri Lanka (see Figure 5).

Geological setting

The project is located within thehighlands that lie in the Balangodaregion of the central highlands of SriLanka.

The reservoir is situated in the‘Highland Complex’ with theunderlying rock types comprising

metamorphic rocks, includinggranulate gneisses, charnockite,marble and dolomitic marble.These rocks are overlain by a thickweathered layer.

The dam’s right abutment and rightrim areas consist of karstic terrain.Karst conditions develop from thedissolution of the host rock alongfractures, joints and/or beddingplanes which become enlarged overtime from the saturation and flow of

groundwater along these features.In addition to karstic conditions,the right abutment and right rimareas have been subject to extensivefolding, faulting and hydrothermalreactions, making the right abutmentand right rim areas geologicallycomplex.

During the investigation andconstruction phases of the reservoir itwas recognised that karstic featureswere likely to be common in the right

bank. The right abutment rises upto a peak of elevation of 545m AODand then descends to a low ridgewhich extends southwards to formthe right bank of the reservoir. Thetopography beyond the abutmentis based on saddles; with four lowsaddles located on a ridge within adistance of 2.9km of the dam site.These saddles occur at levels varyingfrom 20 to 60m above the top waterlevel of 460m AOD.

A karstic feature, a cave, wasdiscovered during the constructionphase 300m upstream of theproposed axis of the dam on theright abutment. This cave appearedto form along a minor fault, one of

Figure 5. Photograph of Samanalawewa Dam


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Figure 6 presents an interpretationof Survey 1 results. This figure showsthe positions of the ECF modelledflow paths (vertical and horizontalalignment).

It appears, based on these postedelevations, that seepage north ofthe tunnel is near the elevation ofthe reservoir level at the time of thesurvey (about 440m). The modelalso suggests that seepage north ofthe tunnel occurs above the tunnel

and finds an opening in the adit’sgrout curtain very near the 440melevation. Seepage south of thetunnel flows a few metres deeperat elevation 438m. At the locationwhere the two flow paths converge,east of the adit, the elevation ofthe preferential flow path drops alittle more rapidly as it flows to thedischarge point out of the hillside.It is important that all elevations, aswell as horizontal positions, are theresult of a relatively inaccurate GPS

grout curtain area. This work waslimited to a minimal number ofmeasurement stations and wasdone to investigate whether or notseepage was a problem through thegrout curtain. The intention of theadditional work was not to detail ormodel seepage flow paths throughthe right rim grout curtain. Rather,it was to identify if major seepagepath(s) exist through the groutcurtain and if so, to determine whatadditional work should be performedto fully characterise seepage throughor beneath the right rim’s groutcurtain study area.

In performing the two surveys, aninjection electrode was placed in thereservoir (some distance from theupstream face of the dam and rightrim area). A return electrode wasstrategically placed in contact withseepage flowing from the hillsidedown-gradient of the embankment.

clay, the leak was not stopped. Noreduction was noted after the firstphase dumping but after the secondphase, it was reported that the clayblanket helped reduce marginally thegroundwater pressure in the rightabutment.

Willowstick surveylayout

The Willowstick investigation of the

right abutment study area employedone horizontal dipole electrodeconfiguration to energise thesubsurface study area. The originalscope of work was limited to onlyone demonstration survey.

Shortly after the fieldwork wasinitiated and based on preliminaryresults, Willowstick suggested asecond survey. This second surveywas targeted to investigate possibleseepage through the right rim

Figure 6. ECF Model with Posted Elevations


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Conclusion

The Willowstick technique allowsindividual flow paths to be mappedboth in plan and elevation at depthsin excess of 200m to an accuracy of0.1m. This enables remedial worksto be focused on the areas of defectand generate savings of millions ofpounds on large schemes, wherewithout this knowledge, extensivegrouting or cut-off construction

schemes would be necessary.

End note

The Willowstick technique can andhas been used in a number of otherfields where the passage of waterneeds to be traced. Examples wouldbe the tracing of groundwater intoexcavations or tunnels, loss of waterfrom canals, environmental pollutioninto bodies of water, and even

tracing deposits of gold in waste tipswhere the water which is sluicedonto the tips adheres preferentially tothe gold!

through karst topography needs tobe carefully characterised, monitoredand possibly remediated to ensurethe integrity of the reservoir aswell as the safety of those residingdownstream of the dam.

Remedial works

The Willowstick survey has confirmedtwo main areas where the cut-off iscompromised – one on the bend of

the tunnel and the other where theoriginal cut-off crosses the tunnel.Having identified the location ofwhat are believed to be the twolargest sources of leakage throughthe right abutment area, it is possibleto undertake cost effective remedialworks at the Dam to ensure thesafety and integrity and to bring thereservoir back to its proposed topwater level and so retain its ability togenerate energy.

The work will involve measures:1. to close two significant gaps in

the existing supplementary groutcurtain

2. to locate and fill major karsticfeatures at approximate elevationof 438m.

data set. Nevertheless, the data stillprovide a good indication of howseepage flows past the dam.

Seepage through the open gap inthe tunnel’s grout curtain appearsto be slightly below reservoir waterlevel as well. Had the grout curtainbeen placed below the tunnel inthe gap, seepage would still havepassed through this area because theseepage flow is above the tunnel.Where the grout curtain was placed

above the tunnel, just west of theadit’s grout curtain, seepage is splitby the upward vertical grout curtainand some flows through the aditgrout curtain and some flows southof the tunnel around the adit’s groutcurtain.

In conclusion, the results of theinvestigation suggest that there isa series of braided seepage flowpaths north and south of thetunnel that run beneath the right

abutment study area. Seepageappears to concentrate around theright side of the dam rather thanunderneath or through the dam’searthen embankment. There is someseepage occurring along the rightrim grout curtain, but not to theextent that it is flowing through theright abutment study area. It hasbeen recommended any seepage

Acknowledgement

The paper was presented and published in the proceedings of The British Dam Society 16th Biennial Conference held inGlasgow 2010.


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Background

Atkins ecologists first came acrossRoman snails in early 2009,when working on behalf of theHighways Agency, undertaking anEnvironmental Assessment as partof proposals for the installation ofnew gantries along a stretch of theM25 motorway in Surrey (the M25Controlled Motorways scheme). Anempty Roman snail shell was foundduring an extended Phase 1 habitatsurvey, at the base of a steep chalk

section of the motorway vergebetween junctions 7 and 8 of theM25. On a subsequent nocturnalsurvey a live individual was found,in an area of long, semi-improvedgrassland with dense patches ofbramble, close to junction 8. Atkinsecologists have also found Romansnails on another section of the M25motorway (close to junction 6), whenworking on a separate project forthe Highways Agency. Shells werefound within plantation woodlandon the verge and live individuals havebeen spotted numerous times in thetussocky grassland situated directlybehind the woodland.

As a result of these findings, anda need to resolve the issue of thepresence of this legally protectedspecies within proposed constructionareas for the above scheme, furthersurveys have been carried out andappropriate licences sought.

Habitat requirementsand distribution

The Roman snail is known to inhabitopen woodland, rough and tussockygrassland, hedge banks, chalkquarries and areas of scattered scrub.Figures 1 and 2 show the areas ofthe M25 motorway verge whereRoman snails have been found.

This species requires loose, friablesoil for burying into for hibernationand also for depositing eggs. Lime-rich, free draining soil is a habitatrequirement in the UK and studies

have found a preference for south-facing slopes1. Roman snails willnot occur in sandy soil. They willalso avoid grazed grassland and veryopen, exposed habitats.

Roman snail: An introduction toits ecology and legal protection

Abstract

In 2008, the Roman snail Helix pomatia was added to Schedule 5 of theWildlife and Countryside Act 1981 (as amended), and it became an offenceto intentionally kill, injure or take individuals of this species (as did possessionand sale). Also known as the ‘edible snail’, the primary reason for its legalprotection in England and Wales (and elsewhere in Europe) was an increasing

trend in collection of large numbers by amateur cooks and for commercialuse in restaurants. However, the legal protection this species is now affordedhas implications for development projects. Distributed throughout south-east England (but especially the North Downs) and through the Chilterns andCotswolds, and occupying a broad range of habitats (where suitable soilsare present), this species could occur on a wide variety of sites. This articleprovides an introduction to Roman snail ecology and licensing requirements,and illustrates these using a case study in Surrey – the M25 ControlledMotorways Scheme.

Figure 1. Roman snail habitat on M25verge

Figure 2. Roman snail habitat on M25verge


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Identification

Adult Roman snail shells are typicallylarger than those of other snailspecies in England, measuring upto 5 cm across and displaying a

pattern of brown bands (see Figure4). Crucially, the bands on their shelllack the zig-zag pattern found onthe garden snail Cornu aspersum (= Helix aspersa - see Figure 5). Thebody of the Roman snail is pale greyand measures up to 10 cm long onadults.

Empty Roman snail shells oftenappear very pale and lack the browncolouration shown in Figure 4, as do juvenile Roman snail shells (shown

in Figure 6). Empty shells become‘bleached’ and in this state areusually more than one year old4.

Figure 3 shows a UK distributionmap for Roman snail2. The species isnot native to the UK and is thoughtto have been introduced by theRomans. Much of its distribution inthe UK is considered likely to be dueto local introductions by humans.There are documented introductionselsewhere in England and also inScotland and Ireland, and these arestill shown on some distributionmaps, but these introduced animalsrarely survived for very long2. Thiswas presumably because soil and/orweather conditions were not suitable.The main hotspots for populationsof Roman snails in England arealong the North Downs (from Surreyto Kent), the Chilterns (especiallyin Hertfordshire) and throughoutthe Cotswolds and Mendip Hillsfringes. There are also documentedpopulations in Cambridgeshire.

Life history

Many aspects of the Romansnail’s life history and behaviourcontribute to its vulnerability toover-exploitation. In particular,their tendency to aggregate in highnumbers and disperse only shortdistances leaves them vulnerableto collection. Individual snails mayspend their entire lives within an areaof approximately 30m in diameterand take two to five years to reach

maturity and reproductive successmay be low, with many Britishpopulations found to have a lowproportion of young snails3.

In England, Roman snails are typicallyactive from May to August. Theearliest and latest dates for activity inan area of the Cotswolds were April30th and September 1st 3, with peaksin activity most likely in May andJune4.

Roman snails hibernate in the groundby digging down into loose soils,pulling vegetation and soil over thetop to close the top of the entranceto their chamber. They remain inhibernation until spring.

Figure 3. Distribution map for the Roman snail, from Kerney (1999)

Figure 4. Adult Roman snail(Photograph: Dr Martin Willing)

Figure 5. Roman snail shell (left), gardensnail shell (right)


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hours or be humid and it should alsobe warm.

A juvenile Roman snail was foundduring the torch survey for the M25Controlled Motorways project.

Legislation andlicensing

Roman Snail was added to Schedule5 of the Wildlife and Countryside Actin April 2008. It is not a EuropeanProtected Species, although it does

receive legal protection in otherEuropean countries. In the UK, itis protected in relation to Section9(1), (2) and (5) of the Wildlife andCountryside Act only. This meansthat it is an offence to intentionallykill, injure or take this species. It isalso an offence to possess a live ordead Roman snail (possession is onlyan offence if it has been illegallytaken from the wild) and it is alsoprotected against sale. It is not an

offence to disturb Roman snail or todamage or destroy breeding placesor resting places of this species.However, although disturbance isnot an offence, a licence is neededto handle Roman snails, howeverbriefly, because it is protected against

In larger areas of habitat, attentionwould best be focused on log pilesand areas that could provide refuge(see Figure 7). This is best carriedout during the snail’s active period(May to August), after recent rainfall,especially in warm, humid conditions.Individuals will bury into the topsoilduring prolonged hot/dry spells. Atsites with well-established colonies,evidence of Roman snail presencecan be found at anytime of the year,in the form of empty shells.

The tendency for Roman snails toaggregate in high numbers and thelongevity of their shells means thathand searching over relatively smallareas is an effective way to search forevidence of this species.

Torch surveys

In areas deemed potentially suitablefor Roman snails, a nocturnal surveywas also carried out in June, in orderto look for active Roman snails. Idealtiming for torch surveys is late April

to early June. This involved searchingareas with a powerful torch at leastone hour after sunset. This surveytechnique relies on appropriateweather conditions; it must beraining, have rained in the last 24

Surveying for Romansnails

Whilst no standard publishedsurvey technique for Roman snailscurrently exists, it is considered thatthe combination of careful handsearches and one or two nocturnaltorch surveys in suitable weatherconditions, as described below, will

allow an assessment of presence orabsence of Roman snail at a site.

Daytime hand searches

Two survey techniques were usedby Atkins for the M25 ControlledMotorways scheme, once thepresence of the species hadbeen confirmed, following theidentification of an old shell duringthe initial extended Phase 1 habitatsurveys in 2009. Hand searches ofareas of habitat to be affected werecarried out. This involved searchingthrough areas of long grass andscrub by hand, looking for Romansnails and old shells. Particularattention was paid to searchingunderneath logs, brash and artificialrefuges present on the verge of themotorway. Some gantry locationswere ruled as not suitable for thespecies due to the presence of sandysoils. This hand searching techniquewas effective because each of the

footprints for gantry constructionwere relatively small; the workingarea for each gantry footing (i.e.total vegetation clearance) was amaximum of ten metres by fifteenmetres (150m²).

Figure 6. Adult Roman snail shell (left), juvenile Roman snail (right)

Figure 7. Hand searching for Roman snails


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Acknowledgements

Thanks to colleagues John Box FIEEM and Jules Wynn MIEEM for providingconstructive reviews of the script. Constructive comments from MartinWilling, Conservation Officer of the Conchological Society on a draft of thispaper are gratefully acknowledged, as is assistance with field study techniquesand habitat recognition on the M25 project. A version of this paper wasoriginally published in In Practice (2011, 72, 26-29) and their permission toreproduce it here is gratefully acknowledged.

References

1. Pollard E (1975) Aspects of the Ecology of Helix pomatia L. Journal ofAnimal Ecology, 44: 305-329.

2. Kerney M P (1999) The Atlas of the Land & Freshwater Molluscs ofBritain and Ireland. Harley Books, Colchester

3. Alexander K N A (1994) The Roman Snail Helix pomatia L inGloucestershire and its conservation. The Gloucestershire Naturalist7: 9.

4. Dr Martin Willing, Conchological Society, (pers. comm.)

a base-rich, friable topsoil. In moreopen areas, creating more coverthrough planting of scatteredscrub, or relaxation of managementregimes could deliver enhancements.Woodland edge could be improvedthrough the creation of ecotonehabitat where this does not alreadyexist.

The above application was grantedby Natural England. However,subsequently a decision was taken

by the Highways Agency not to buildnew gantries in this part of the M25Controlled Motorways scheme and,therefore, this licence will not nowbe implemented.

Summary

The Roman snail is a relatively easyspecies to identify once familiar withits characteristics. Identifying thepotential presence of the species can

be achieved through understandingof its habitat requirements and willbe aided by the fact that, broadly, itsdistribution is quite well understoodand likely to be relatively unchangingin England due to its inability tocolonise new areas quickly. However,increased surveying and reportingfor the species, now it is legallyprotected, could lead to amendmentsto the distribution map and it would,no doubt, be beneficial to sendrecords to local biological recordcentres and to the ConchologicalSociety of Great Britain and Ireland.

Dealing with Roman snails ondevelopment sites is relativelynew and mitigation and habitatenhancement measures are currentlylargely untested. Collation ofinformation from future projects willenable ecologists and stakeholdersto refine techniques and testnew approaches. As with habitatenhancements for other species,measures to improve habitats forRoman snails are likely to lead tobenefits for other species in the localarea.


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continual working with the client

representative. Preferred solutionswere selected using a risk-basedapproach to design developmentand decision making taking anactive consideration of residualrisks. This was particularly relevantas the preferred solutions were tostrengthen existing assets rather thanbuild new. During construction,a rigorous culture of challenge toany proposed changes and riskmitigation options was developedto ensure that value for money was

maintained through to completion ofthe scheme.

was supported by selected specialist

contractors as the key designand construction elements weredeveloped and delivered.

The integrated team approach wasthe key to successful delivery of theproject and crucial to this was thedevelopment of a highly performingteam with the appropriate cultureand attitude. The team developedwith a common understandingof the aims, objectives, desiredoutcomes and concept of the

scheme. The approach was toencourage integration of the designteam and the contractor’s temporaryworks team to develop practical,safe and efficient solutions andconstruction methods and included

(Figure 1). This pattern has arisenfrom the pressures on space alongthe river from commerce anddevelopment. Gainsborough isparticularly vulnerable to floodingdue to the meeting of tidal andfluvial floodwaters, and the low-lyingnature of the town and buildingsthat are located close to the river.

Following a series of conditionsurveys and studies, it wasestablished that generally, with the

exception of one failed wall, theexisting flood defences did not showsigns of major distress. However, theanalysis indicated that many defenceswould fail under worst credibleloading conditions, i.e. during andafter prolonged flooding. For eachindividual flood defence optionswere considered to replace, improveor continue to monitor the asset.Assessment was made of the residualrisks and consequences associatedwith each option for considerationby the Environment Agency, so that adecision could be made on the mostcost effective way forward.

The use of a detailed conditionassessment coupled with numericalanalysis, enabled the tabling ofa strategy to re-use many of theexisting flood defences includinglarge areas of sheet piles, most ofwhich were originally thought to beat the end of their design life. By

balancing cost and risk, a sustainableand cost effective approach forensuring the continuity of floodprotection to Gainsborough wasdeveloped.

Construction works commencedin June 2006 and were completedin September 2010. The workswere designed and delivered by anintegrated project team, comprisingthe client, designer and contractor.The core team was drawn from

Environment Agency frameworkpartners. This facilitated thedevelopment of the integrated teamapproach as the team members werefamiliar with the client’s objectivesand procedures. The core team

Figure 1. Typical river frontage in Gainsborough


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flood risk were identified and risksattached to each of the options werediscussed. The consequences of anyfailure of the walls and defenceswere then reviewed to ensure thatacceptable solutions were chosen.

The main outcome of this work wasthat for the existing mass gravity walldefences, it was deemed appropriate

to implement a monitoring regimeto identify further deterioration oftheir condition. If deteriorationwas identified then a programmeof improvement or replacementworks would be developed at that

that, rather than replacement, theresidual life of most of the flooddefences could be extended byimplementing strengthening worksand improvement measures. Thebenefit was a reduced use of naturalresources, lower construction costand less impact to the riversidecommunity.

The project team, incorporating theend user and specialist contractorsalongside the designer, developedinitial outline designs and budgetsto identify options for improving thedefences. Options for managing

History of floodingand flood alleviationschemes inGainsborough

As a consequence of the majorfloods in 1947, a flood relief schemefor Gainsborough was implementedin the early 1950s to give addedprotection to the town. This schemeprovided a rigid flood defence alongthe river frontage of the town, withmany of the defences constructedon existing structures, some ofwhich were already over 100 yearsold. A significant tidal surge in 1954resulted in the defences being raisedfor a second time, usually in the formof additional concrete capping toexisting river walls and frontages.

In 1990/91 the Environment Agency’spredecessor, the National RiversAuthority, commissioned an assetsurvey. The survey concluded that,having been in place for over fortyyears and in most places beingfounded on original structures,the defences were unlikely to lastmore than five years and withoutintervention were likely to fail.

Works to replace 800m of theexisting defences that were in theworst condition were completedin 2000 at a cost of approximately£20 million. These works includedtraditional new sheet piled wallstogether with a piled free-standingstructure in the bed of the river. Theremaining assets, which were notthought to be in urgent need ofrepair in the early 1990’s, were thesubject of the recent scheme.

Asset condition surveyand appraisal

In 2004-05 an asset conditionsurvey was undertaken on theremaining original defences. Thesurvey established the residuallife of the flood defences anddevised a strategy for improvementworks. The assessment concluded

Figure 2. Existing mass gravity flood wall with significant cracking


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management and reduction of theongoing risks. Consequently duringthe development of the scheme, theteam ensured that they establisheda thorough understanding of riskthrough investigations, design andrisk workshops.

Consultation regarding the projectrisks led the team to develop thesolution to allow the continued

use of the existing defences. Thisrisk based approach, i.e. balancingthe cost of improvements againstresidual risks and consequences, wasembraced by the team and clientthroughout the life of the scheme.

• The expectation that existingstructures could only takelimited additional loading duringconstruction.

• Many of the working areas wereconstrained by existing propertiesand structures.

• The River Trent is tidal and subjectto a large range of river levels and

poses the risk of both fluvial andtidal floods.

Early on, the project team recognisedthat successful delivery of thescheme within budget requireda continuing understanding,

time. This approach deferred theneed for a capital replacementscheme for these assets. For theexisting anchored sheet pile wallsand the earth embankments, theconsequences of further deteriorationand their possible failure weredeemed unacceptable. Therefore ascheme of remedial works to extendthe life of the assets was developed.

An economic appraisal of whole lifecost and present value, comparing

new walls against remedial works toextend life of assets and then replacein 20 or 30 years, confirmed thatimplementing remedial works nowwould be the best economic option.

The main improvement worksrequired by the preferred optionwere:

• Replacement of 50m of failedmass gravity floodwall (Figure3) with a new anchored steelsheet pile retaining wall and flooddefence.

• Installation of a plastic sheet pileseepage cut-off to increase thestability of 1.7km of existing earthembankments (Figures 3 and 4).

• Raising 550m of earthembankment to increase thestandard of flood protection froma 1 in 70, to a 1 in 200 annualchance event.

• Installation of 441 groundanchors and associated steelworkto strengthen 730m of harddefences to reduce the risk offailure (Figures 5 and 6).

Risk based approachand team work

The nature of the works atGainsborough meant that thereare a significant number of risks to

manage. Of primary concern was:• Working with existing riverside

retaining structures with onlya limited knowledge of theirconstruction and condition.

Figure 3. Existing earth embankment flood defence in poor condition

Figure 4. Existing earth defences were strengthened using a plastic pile cut-off


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This decision led to a significantreduction in the time required foranchor testing. This was particularlybeneficial as the testing of individualanchors was constrained by theavailability of suitable workingwindows between the tides. Typicallythis window could be as little asone to two hours, giving a testingrate of only two per day. Followingtesting of the first sets of anchorsinstalled, we were able to reduce thefrequency of testing to an averageof 5% and 10% (bottom row andtop row of anchors). This reductionled to a saving of five months onthe overall construction programme,contributing to the overall cost savingon the scheme.

Sustainability andinnovation

In delivering the scheme the focus

was on maximising value whilstensuring the upgraded assets weresustainable in both design andconstruction. The very nature ofdelivering the works whilst strivingfor value and sustainable solutionsencouraged innovative ideas fromthe team for both permanent andtemporary works. This approachto value engineering and opennessto the use of innovation was thekey to successful project delivery.Understanding product function and

looking at how best to achieve thisfunctionality always remained at theforefront of the team’s thoughts.This section highlights some of themain sustainability and innovationachievements of the scheme.

Plastic piles

The use of plastic piles to strengthenthe existing earth embankmentsprovided an alternative to widening

of the embankments and minimisedthe amount of imported materialrequired (Figure 7). This use ofplastic piles, containing recycledmaterial, was one of the first forthe Environment Agency and

the frequency of anchor acceptancetesting. The team had recognisedthat applying existing design codesfor anchor testing to the remedialworks was not directly appropriate.A more relevant testing regime wasthen developed in conjunction withthe end user to balance constructionrisks and costs against therequirement to ensure satisfactoryperformance of the installed anchors.

The team worked to mitigate risksin both the permanent works andin particular the temporary worksused for construction. Without thiscommitment from all parties to a riskbased approach, the project wouldnot have delivered the innovativesolutions to improving the defences.

An example of the risk basedapproach was a decision to reduce

Figure 5. Existing anchored sheet pile walls in visually poor condition

Figure 6. Existing frontages were strengthened using one or two rows of groundanchors with waling beams; fenders protect the finished works from river traffic


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the estimated residual life of thestrengthened frontages. Howeverit was still assessed to be the mostsustainable and preferable solution.

Design refinement

For waling beam installation(Figure 9) to ensure an even loaddistribution between the new beamsand the existing sheet piles, thedesign required a packing material(Figure 10). The original design wasbased on the use of prefabricatedsteel packers. Due to the varyingshapes, position and alignments ofthe existing piles, each packer waspotentially unique requiring bespoke

manufacture. During construction aninvestigation into possible alternativesolutions was undertaken. Thisidentified grout and epoxy resin bagsas a viable cost effective alternative,a technology borrowed from bridgeengineering. The solution provides

This would significantly increase thescheme costs by around £3 millionand take it above the approvedbudget. More importantly, theuse of cofferdams would generateincreased health and safety risks. An

alternative would have been to revertto a traditional new build that wouldhave lost the sustainable benefits ofreusing the existing assets.

To ensure the scheme remainedviable and that risks were avoided,the team revisited the concept anddesign of the strengthening worksin conjunction with the end user. Byusing the improved understanding ofthe river levels and available workingwindows, a modified scheme was

established that still achieved thedesired outcomes. This was achievedby redesigning the strengtheningworks with the bottom row ofanchors installed at a higher level.This had the effect of reducing

Tidal monitoring continuedthroughout the construction phaseand this supported an effectiveand efficient resource programme.The monitoring gave the team abetter practical understanding of

how the river responded to tidesand fluvial flow conditions. Thisallowed productivity to be maximisedenabling the main strengtheningworks to be completed ahead ofprogramme and at a reduced cost.

Design change

At outline design stage theavailable information on river levelsindicated that it would be possible

to install low level anchors duringnormal tidal windows. However,the tidal monitoring informationdemonstrated that to implementthe original design proposals wouldrequire significant temporary worksin the form of cofferdams in the river.

Figure 8. Temporary working platform to allow for installation of ground anchors over the tidal River Trent


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savings and reductions in installationtime, material cost and carbon costas well as a reduction in health andsafety risks compared to the originalproposal.

Through the efficient use ofmaterials additional savings weremade. The original fender designrequired bespoke fenders at eachlocation, 630 fenders in total.This was due to different lengthsrequired to fit the varying shape

of the existing frontages. Thedesign was revisited, with additionalsurvey information on the sheet pilegeometry, to develop a simplifiedfender solution which could beused consistently throughout thescheme. This reduced the numberof different fender sizes required andimproved the efficiency of fabricationand installation. As part of thisdesign development process thedesigner and contractor developedfixing methods that would allowinstallation in a quick, easy and safemanner (Figure 11).

A further review of the requirementfor fenders to afford protection tothe anchor heads from accidentalriver vessel impacts generated asignificant change in the projectteam’s understanding of the system.The result was to reduce the fenderrequirement at each anchor from twoto one, decreasing the total number

of fenders by 300.

Handover

Due to the fragmented locationsof the various assets and the largenumber of individual operations, anadvanced asset pre-handover andcompletion programme was created.This enabled earlier inspectionsof assets and individual workprocesses. The advantage of thiswas in reducing any potential delaysand additional costs at the end ofthe scheme. Due to the constraintsof tidal working and the need forspecialist temporary works, it waspreferable to maintain continuity of

Figure 9. Installing prefabricated waling beam sections – packers are requiredbetween the beams and the existing piles to ensure an even transfer of loads

Figure 10. Completed section showing waling beam, grout packers and fenders


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working and to avoid the need forany separate remobilisation.

Summary

The key to successful deliveryincluded the development of ahighly performing team with theappropriate openness, willingnessto be challenged, culture andattitude. The team developed acommon understanding of the

aims, objectives, desired outcomesand concept of the scheme. Theapproach was to encourage theintegration of the design team andthe contractor’s temporary worksteam to develop practical, safe andefficient solutions and constructionmethods.

Maintaining close communicationwith the client has been fundamentalto success. The development oftrust and the transfer of knowledge

and understanding has facilitateda risk-based approach to designdevelopment and decision making.Overcoming problems and risks jointly as a team meant that bettersolutions were quickly found andavoided unnecessary and abortivecosts. A rigorous culture ofchallenge to any proposed changesand risk mitigation options wasalso developed to ensure value formoney throughout the design andconstruction of the scheme.

The Gainsborough flood alleviationscheme was a large complex projectthat used an innovative approach tothe continual management of floodrisk by extending the life of existingassets. The nature of the worksmeant that there were a wide rangeof risks to manage. By developing ateam with the appropriate skills andapproach, the scheme has been ableto successfully manage risks, identifyopportunities to improve the valueof the works, and work successfullywithin the community to deliver theworks safely. An integrated teamadopting a risk-based approach wasthe key to this success.

Figure 11. Installing fenders using the quick fixing methods developed by the team

Acknowledgement

This article was first published in Proceedings of the ICE - Civil Engineering,Volume 165, Issue 5.


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of North Slope climate collected froma suite of general circulation models(GCMs). These GCMs have all beenrun according to varying globalgreen house gas control scenarioslaid out by the United Nation’sIntergovernmental Panel on ClimateChange1.

The lake forecasting process usesa multiple GCM models, each withmultiple GHG scenarios to createan ensemble of possible future

conditions. The process uses thewater budget model to create aforecast of lake storage based oneach of the GCM model-scenariopairs. Through assessing the rangeof possible future lake storage levelsprojected by the GCMs, researcherscan build understanding of if climatechange will have a net drying orwetting effect.

In terms of ice road planning, a waterbudget model is created for each

lake that stakeholders – oil firms,regulatory agencies, tribes, etc. –plan to use to build the ice road.Using the storage forecast results forthese lakes, stakeholders can assessthe risk of the lakes being unable toprovide sufficient water for ice roadconstruction, and use this risk in theirdecision making process.

Water budgetformulation

Water budget models in the NSDSSare specific to the arctic environmentof the North Slope. The followingformulation begins with a generalwater budget modeling approach,and then customizes it to theseasonal arctic cycle of freeze andthaw.

A water budget model for a lake andits watershed can be defined as in Equation 1, where DS is the changein storage for a given time, Q is thenet flow out of the system, P is theprecipitation flux into the system, ET is the evapotranspiration out of thesystem, and Extraction is the waterused for ice road construction.

Department of Energy’s NationalEnergy Technologies Laboratory, theNSDSS is used by all stakeholdersas a common workbench forexploring options for ice roadconstruction. The NSDSS explicitlyconsiders optimal water use, directand cumulative environmentalimpacts, and multiple objectivesand values among stakeholders.Development of the DSS is acollaborative effort of academic andindustry personnel with significantstakeholder involvement frommultiple agencies of local, state, andfederal government, private energycompanies, and non-governmentalorganizations.

Development of the NSDSS has beenpartitioned among three groups. TheUniversity of Alaska at Fairbanks ledthe overall project administrationand development of natural systemsmodels; Texas A&M University leddevelopment of the optimizationmodels for ice road alignmentplanning; the Atkins team, ledby Stephen Bourne in Atlanta,Georgia in the United States, led thedevelopment of new technologiesand the translation of conceptualmodels developed by the other teamsinto robust software tools.

This paper focuses on the NSDSSwater budget modelling functionality.The water budget model is one of

several natural systems models thatthe NSDSS is capable of producing.Using the NSDSS EnvironmentalAnalyst module, users can createand publish water budget modelsfor any of the thousands of lakeson the North Slope of Alaska. Thewater budget model estimatesthe storage in the selected lake bysolving a seasonal water balanceequation as described in the sectionsbelow. Users have the option toboth conduct an historical analysis

or a future analysis. For historicalanalyses, data from the 30 yearrecord of on-going permanentweather sites plus field surveys isused. For future analyses, the inputdata is a series of possible realizations

Introduction

Alaska’s North Slope hosts a wealthof natural, cultural, and economicresources. It represents a complexsystem, not only in terms of thebiophysical system and its globalimportance but also from thestandpoint of its social dynamic.Stakeholders of the North Slopeinclude oil companies, regulatoryagencies, local tribes, environmental

advocacy groups, and researchers.Domestic energy development onthe North Slope – particularly inlight of changing climate – must beconducted with best managementpractices that will ensure benefitsfor all stakeholders. Establishingthese practices and ensuring theyare followed requires an all-inclusivestakeholder design process; one thatresults in cost-effective developmentstrategies that fit within a broader

context of long term cultural,economic, and environmentalsustainability.

Ice roads provide a cost-effectivemeans of oil and gas explorationwith minimal impact to the sensitiveunderlying tundra. These icestructures have become a necessityfor oil and gas exploration activitieson the North Slope. Due to thelarge volumes of water required toconstruct and maintain ice roads

and ice pads, their constructionand maintenance have becomea challenge to water resourcemanagers. With energy consumptionon the rise worldwide, waterresources managers need a clearunderstanding of the viability andlong-term impact of ice roads and icepads.

The North Slope Decision SupportSystem (NSDSS) is a technologicalsolution that brings to bear the

latest data storage and service,natural systems modeling, anddecisions support and collaborativemanagement theories in support ofoil and gas exploration. Developedunder a research grant from the U.S.


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Data sources

The NSDSS water budget model hasthe ability to do historic models andforecasts. For historical analysis, fielddata contained within the NSDSSdatabases is used. For forecasts,projections from General CirculationModels (GCMs) are used. Thehistorical field data in the NSDSSstretches from approximately 1980 topresent. The GCM data used in the

NSDSS typically stretches from 2001to 2100.

Using GCMs for climate changeimpact forecasting is becomingthe current state of the art. GCMsare global numerical models of thecoupled atmospheric-ocean-landsystem. They discretize the globewith grids that stretch from the Northto the South Pole with grid-cell sizesof approximately 2 degrees latitudeand longitude. They are typically run

over time frames of many centuriesat hourly time steps. Each GCMmodels hundreds of physical andchemical variables in the globalsystem and produces statistics ofthose variables. The NSDSS uses themonthly total liquid precipitation

Equation 5:

S lake

(t+1) = S lake

(t) + P lake

(t)∙Alake

- a[P wshed

(t)-ET wshed

(t)]Awshed

–

E lake

(t)∙Alake

– Extraction(t)

Annual cycle – Alternatingrunoff coefficient

The annual North Slope hydrologiccycle is punctuated by two events,spring thaw, and fall freeze up (seeFigure 1). The water budget inequation 5 above must thereforebe split into two seasons, one fromspring thaw to freeze up, and theother from freeze up to spring thaw.

The runoff coefficient, a, differs forthe two seasons. At spring thaw,the runoff coefficient is very high(e.g. 0.9) because the snow meltoccurs over a few days. Over thesummer season, however, a muchlower coefficient is applied (e.g.0.4) as movement of water occurs

much more slowly and there ismore opportunity for groundwaterseepage and movement of water toneighboring watersheds. The runoffcoefficient must therefore alternatefrom spring thaw (0.9) to summer(0.4) in the seasonal calculation ofthe storage time series.

Equation 1:

DS = P - Q – ET - Extraction

To establish water dynamics,Equation 1 can be converted to astate space form as follows, wheree is an error term associated withunaccounted fluxes, or systematicerrors in the measurements of eachflux term.

Equation 2:

S(t + 1) - S(t) = P(t) - Q(t) – ET(t) –

Extraction(t) + e

Focusing on the lake itself, and thestorage available for building iceroads, we can split equation 2 intoequations focused on the lake andthe watershed, respectively:

Equation 3:

Lake: S lake

(t+1) – S lake

(t) = P lake

(t)∙Alake

- Q lake

(t) - E lake

(t)∙Alake

– Extraction(t)

+ e lake

Equation 4:

Watershed: S wshed

(t+1) – S wshed

(t)

= P wshed

(t)∙Awshed

- Q wshed

(t) -

ET wshed

(t)∙Awshed

+ e wshed

Note that the evaporation term forthe lake is simply the evaporationfrom the lake open water body. Notefurther that the precipitation andevapotranspiration/evaporation termsare typically measured as depths, andtherefore must be multiplied by thearea of lake or watershed to derivevolume.

The following assumptions are made:

1) The flow into the lake, Qlake

, isequal to a fraction of the NetBasin Supply from the watershed.Assuming watershed storagestays constant, we can then say:

Q lake

= aQ wshed

= a(P wshed

- ET wshed

)

Awshed

2) The error terms are zero,

The Lake storage is therefore:

Figure 1. Annual North Slope Hydrologic Cycle (from Tidwell, 20092)


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over the lake and over the watershedis calculated by converting the snowdepth at the time of spring thawwith a user-specified coefficient(default = 0.15 for both lake andwatershed).

For forecast data, since the GCMprecipitation flux term is an estimateof liquid water, no snow-to-liquidwater conversion is necessary.

Fall freeze up trigger

Similar to the definition of startof spring thaw, the winter seasonis defined as starting when thetemperature goes below a user-specified level (-5 deg. C by default).

Trigger search method

In each year, the spring thaw andfall freeze up triggers are unknown.Indeed, with the GCM-basedforecasts, it is possible that a fallfreeze up may not occur at all. To

find the triggers, the NSDSS uses thefollowing algorithm:

1) For each year in the time series

2) Starting in October search eachmonth until the temperature fallsbelow the freeze up trigger.

3) Define the month when thefreeze up trigger occurs as thestart of winter.

4) Starting from the start of winter,search each month until the

temperature goes above thespring thaw trigger.

In the event that the fall freeze-updoes not occur, no winter seasonis defined for the year in question.That is, the entire year is treated as asingle non-freezing season.

Splitting the waterbudget into winter-timeand summer-time

The water budget in equations4 and 5, must be split into twoequations each, one for winter-timeand one for summer-time as follows:

from multiple centers to derive acomprehensive forecast of globalclimate. In this NSDSS water budgetmodel, the following GCM modelresults are used. The data fromthese models was downloaded fromthe North Slope Decision SupportSystem’s GCM data web service4,the data from which was originallydownloaded from the IPCC datacenter.

• ECHAM5/MPI-OM (2004)

from the Max Planck Institute,Hamburg, Germany

• MIROC3.2(2004) from the Centerfor Climate Research, Tokyo,Japan

• HadCM3(1998) from theMeteorology Office, Devon, UK

• CNRM-CM3(2004) from theCentre National de RecherchesMeteorologiques, Toulouse,France

Time stepconsiderations

For historic analysis within the NSDSSwater budget model, field data isused, which typically is recorded ata daily time step, though sometimessub-daily data is recorded as wellas data at irregular time stepsduring snow surveys. For futureanalysis, monthly time step data is

used from GCM model results. Toestimate seasonal fluxes, this data isaggregated up to the seasonal scale.The start and end of seasons isdefined using the following triggers.

Spring thaw trigger

Spring thaw occurs at differenttimes each year depending on manyfactors. To estimate the flux of liquidwater from snow at the beginningof spring, the depth of snow at the

start of spring thaw must be known.The start of spring is defined withinthe NSDSS model as the period whenthe temperature rises above a user-specified level (5 deg. C by default).

For historical data, the liquid water

and temperate in the GCM cells thatoverlie the North Slope as the basisfor lake water budget forecasts.

The GCMs are intended tosimulate the globe under severalfuture green house gas emissions(GHG) regulation policy scenarios.The scenarios are set by theIntergovernmental Panel onClimate Change (IPCC), which wasestablished by the United NationsEnvironment Programme and the

World Meteorological Organization,and is considered the leadinginternational body for the assessmentof climate change.

The scenarios were set in the SpecialReport on Emissions Scenarios(SRES)3. They operate on twospectra – Environmental to Economicand Global to Regional, with thescenarios named according towhere they fall on these spectra. Forexample, an “A” scenario reflects a

world focused on economic growth,while a “B” scenario reflects aworld focused on environmentalpreservation. A “1” scenario reflectsa “flat” world, wh

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