IWP&DC - 2008-03.pdf

I N T E R N A T I O N A L

& DAM CONSTRUCTIONWWW.WATERPOWERMAGAZINE.COM

MARCH 2008

Water Power

RCCConstruction speed in south east Asia


The number one subscription journal for the dams and hydro industry

Seismic analysis

Tunnel headloss research

Seismic analysis


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&DAMCONSTRUCTIONWaterPowerEditorCarrieann DaviesActing EditorPatrick ReynoldsTel: +44 20 8269 [email protected]

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CONTENTS

COVER: RCC dam construction insouth east Asia – see p17

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41

32

DAMENGINEERING

ModernPowerSystemsCOMMUNICATING POWER TECHNOLOGY WORLDWIDE

INTERNATIONAL WATER POWER & DAM CONSTRUCTION • ISSN 0306-400X Volume 60 Number 3 • MARCH 2008 3

46 PROFESSIONAL DIRECTORY48 WORLD MARKETPLACE

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R E G U L A R S

4 WORLD NEWS9 DIARY & TENDERS

F E A T U R E S

INSIGHT12 CDC backs Cameroon project

Development proposals for hydropower in Cameroon areadvancing, including the Memve’ele scheme.

RCC17 The need for speed

Fast construction is vital for RCC dams in tropicalclimates, such as the successful work underway at theSon La and Yeywa projects in south east Asia.

SEISMIC ANALYSIS23 Damage assessment of arch dam, reservoir foundation

In investigating seismic damage assessments of arch dams,including dam-reservoir-foundation interaction, both linearand nonlinear time history analyses are of benefit. Moregenerally, demand-capacity ratios should be determinedfrom earthquake records to support planning.

28 Analysis aspects of dams subjected to strong ground shakingA thorough understanding of the inelastic and nonlinearseismic phenomena from strong ground shaking at dams isprerequisite for nonlinear seimic analysis of the structures.The leading guidance on methods of nonlinear seismicanalysis of dams is presented.

TUNNELLING32 Looking at tunnel roughness

Research on TBM drives in Karahnjukar headrace hasgiven fresh insight into the relationship between frictionalheadlosses and unlined tunnel walls and shotcrete lining.Opportunities for further studies are identified.

TECHNOLOGY38 Alternative protection

A flexible semi-mobile flood protection system could helpaddress failings in traditional flood defences.

PLANNING & PROJECTS41 Renewed promise of tidal power at Severn Estuary

Tempted by the potential supplies of renewable energyin the Severn Estuary, the UK is once again investigatingthe prospects for a major tidal barrage and examining avariety of outline project proposals.

The paper used in this magazine is obtainedfrom manufacturers who operate withininternationally recognised standards.The paper is made from Elementary ChlorineFree (ECF) pulp, which is sourced fromsustainable, properly managed forestation.

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WORLD NEWS

4 MARCH 2008 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

WORLDNEWS

WORLDNEWS

www.waterpowermagazine.com

Investment spend in large hydrowas US$15B-US$20B last year,according to the Renewables 2007

Global Status Report prepared by theRenewable Energy Network for the21st Century (REN21) in collabora-tion with Worldwatch Institute.

Large hydro spend represented17%-22% of the total investment in

renewables in 2007, given the esti-mated range of expenditure in thesector. The capacity of large hydrostood at 770GW to give a totalrenewables capacity of 1,101GW in2007, and this came from a 6GWincrease on the previous year whichitself was 15GW higher than the748GW in 2005, says the report.

Excluding large hydro, investmentreached an estimated US$71B inrenewable power, fuel and heat pro-duction assets in 2007 – and almosthalf of the sum was spent on windpower and 30% on solar photovoltaics.

The figures indicate that even atthe highest estimated level of expen-diture the investment in large hydrolast year was only 60% of that in windand on par with that in solar PV. Windpower capacity was 95GW in 2007,a rise of 21GW, or 28%, on 2006.

Global final energy and electricity

Large hydro spend seen atUS$15B-US$20B in 2007

Malaysian company MegaFirst Corp Bhd (MFCB) hassigned a development

agreement with the Government ofLao PDR for the Don Sahonghydropower scheme.

The plant is expected to have aninstalled capacity in the range240MW-360MW, and will be a run-of-river project with a dam and headpond on the Sahong river. The loca-

Mega First Corp signs deal to build Don Sahong in Lao PDR

MagEnergy sees Ph I refurb at Inga II finished by mid-year

MAGENERGY SAID ITS PHASE 1emergency repairs and refur-bishment works to upgrade

the Inga II hydropower scheme in theDemocratic Republic of Congo (DRC)should be completed by June.

The Canada-based firm said that italso had recently received a measureof further political support for its Phase2 plan to refurbish four more turbinesbut said more support was needed.

Phase 1 involves repairs to threeunits and emergency refurbishmentof one unit – the 172MW, G-23 tur-bine. A year ago the runner of G-23was extracted and MagEnergy saidthen that Phase 1 works were expect-ed to be completed by the end of2007. The budget given then forPhase 1 was US$25M, and no fur-ther details have been issued.

The Phase 2 works had been esti-mated to commence in late 2007and had a budget of US$110M.Again, no further details on thebudget have been given.

Inga II was built on the Congo riverand commissioned in 1982 witheight turbines, but years of reduceddemand and restricted maintenancebudgets cut back the operationaloutput to approximately 350MW.Combined with its sister plant, IngaI, which has six units of 52MW capac-ity, the plants have only had outputsof about 700MW in recent yearsdespite total installed capacity ofmore than 1700MW.

MagEnergy, a unit of MagIndustriesCorp, is performing the refurbishmentunder a public private partnership(PPP) agreement, signed in mid-2005,

with Societe Nationale d'Electricite(SNEL) – the DRC’s electricity com-mission. Following the initial PPP deal,the company was joined in the ventureby South Africa-based IndustrialDevelopment Coporation.

The firms are sharing the pro-gramme costs and a year ago it wasforecast that first revenues from there-commissioning of the units wouldbe this year. The PPP deal includes arevenue-sharing arrangement withSNEL. Consultant Ingerop undertookthe technical studies for the pro-gramme prior to the PPP deal.

Last month, the companyreceived a measure of political sup-por t for its Phase 2 plans in theform of a letter from DRC PrimeMinister, Antoine Gizenga. It saidthe letter was welcome encourage-

tion of the scheme is a 150km roadtrip south of Pakse, the capital ofChampasak province.

MFCB is to undertake the projectvia a Lao PDR-registered special pur-pose company, which would sell theoutput from the plant mainly to thecountry as well as neighbours, suchas Thailand, Vietnam and Cambodia.The plant is to come into commercialoperation between 2013-15.

consumption are still dominated byfossil fuels, in shares of 79% and67%, respectively, in the latest fig-ures given, for 2006. The differencewas taken up by nuclear power asrenewables met 18% of the need forboth global final energy consumptionand electricity supply.

In terms of global electricity supplyfrom renewable, though, largehydropower was still dominant. Thefigures for 2006 say 15% of totalsupply was from large hydro, whichequated to just over four-fifths of therenewables share.

It was small hydro though, thatwas mentioned along with wind, solarand geothermal energy as being ableto offer countries the means toimprove their energy security andeconomic development. Often largehydro is set apart when renewablescapacity or expenditure is discussed

ment but added that there remainedfur ther bureaucratic steps in DRCprocesses to complete before workcould begin.

In 2007, the World Bank approveda grant of almost US$300M to boostthe power market in DRC in line withefforts to rehabilitate the existingInga hydro power schemes. The banksaid that the works on the plants –Inga I and Inga II – would see capaci-ty increased from 700MW to1300MW of reliable production.

Separately, mining group BHPBilliton last year agreed to fund thefeasibility study for Inga III. Followingconcept studies, the feasibility studywas to run alongside plans for a800,000 tonnes/year smelter. Thesmelter would require 2000MW ofpower from the hydroelectric plant.

The project company would havea 30-year concession to build, ownand operate (BOO) the project,which then the scheme would trans-fer to the state.

MFCB said the project develop-ment agreement gives it 18 monthsto undertake feasibility and socio-environmental studies in support ofexamination of the technical andfinancial viability of the scheme.

During the year and a half period,the company also has the exclusiveright to negotiate the terms and con-ditions of the project documents,including: the concession agreement;a shareholders’ agreement; powerpurchase agreements (PPAs); andengineering, procurement and con-struction (EPC) contract; an operationand maintenance agreement; and,financial documents.

in an international context.Chair of REN21, Mohamed El-

Ashry, said: ‘So much has happenedin the renewable energy sector duringthe past five years that the percep-tions of some politicians and energy-sector analysts lag far behind thereality of where the renewablesindustry is today.’

The Renewables 2007 GlobalStatus Report was presented at theWashington International RenewableEnergy Conference (WIREC) inWashington D.C. in early March.

Also at the event, CambridgeEnergy Research Associates (Cera)presented research that classedhydropower as one of two “conven-tional emission-free technologies”that the consultant forecast woulddeliver almost half the extra grossclean power capacity by 2030, theother being nuclear.

WORLD NEWS

WWW.WATERPOWERMAGAZINE.COM MARCH 2008 5

Alstom wins Bujagaliturbine orderACONTRACT TO SUPPLY FIVE

generating units and otherequipment to the 250MW

Bujagali hydropower plant being devel-oped in Uganda has been awarded toAlstom Projects India (API).

Alstom’s majority-owned Indiansubsidiary is to deliver the units andequipment, and complete the orderby June 2011. The order is worth justover US$87M and was awarded byItalian turnkey contractor Salini.

The order is for five 51MW Kaplanturbines, generators, balance of plantand hydromechanical equipment, andto erect, commission and hand over.API is to undertake the order at itsfacility in Vadodara, India.

VA TECH HYDRO HAS WON LARGEorders in Costa Rica and thePhilippines. The Costa Rican

order, valued at approximatelyEuro65M (US$96.3M), is to supplyelectromechanical equipment andother items to the country’s 140MWPirris hydropower plant.

The equipment package includestwo Pelton turbines, valves, genera-tors, steel linings and penstocks.

The contract was awarded by CostaRica’s national power utility InstitutoCostarricense de Electricidad (ICE),and includes the design, delivery,erection supervision and commis-sioning of the equipment package.

Financing for the scheme is mostlyprovided by the Japan Bank ofInternational Cooperation (JBIC).

About three-quarters of ICE’soutput comes from hydropower. In astatement, VA Tech Hydro’s parentgroup Andritz said that the plantwould contribute to transmission gridstability as well as meet growing elec-tricity demand.

Meanwhile, VA Tech Hydro hasbeen awarded the refurbishment con-tract for the Pantabangan plant in thePhilippines by First Gen Hydro PowerCorp, which acquired the facility in2006. The client said the refurbish-ment of the 100MW plant would addapproximately 18MW to the installedcapacity and 25 years to the life ofthe equipment. The first of theplant’s two units is to be refurbishedand upgraded over July-December2009 and the second unit is expect-ed to be completed a year later.

The plant was built in 1977 andwas the first significant facility ownedby the National Power Corp (NPC) tobe sold by the Power Sector andLiabilities Management Corp (Psalm).First Gen noted that the plant will alsobe among the first of the plants thatwere sold to undergo refurbishment.

First Gen bought the Pantabanganplant along with the Masiway facility,which have a combined capacity of112MW. The purchase price wasUS$129M in September 2006. Inlate 2006, the initial plan was to add30MW to Panabangan – 15MW toeach of the 50MW units.

Beyond the refurbishment andupgrade, First Gen was also lookingto install additional units at eachplant capable of producing 65MWand 13MW, respectively.

The hydropower project is beingdeveloped by Bujagali Energy Ltd (BEL),which is a JV between Kenya-basedIndustrial Promotion Services (IPS)and US-based Sithe Global Power.

The European Investment Bank(EIB) has signed a Euro92M(US$135M) loan to help fund theconstruction of the scheme on theupper Nile river.

Bujagali has been under develop-ment since the 1990s and the devel-oper changed. Last year support fromthe World Bank unleashed a wave ofsupport from other banks and agen-cies. Construction work started in thelast half of 2007 and the scheme isto be commissioned in 2011.

GAMMON INFRASTRUCTUREProjects Ltd (GIP) plans to usefunds raised through its forth-

coming stock offer to help financethe development of the Rangit IIhydropower project.

The 60MW Rangit II scheme is tobe developed on the Rimbi river, a trib-utary of the river Rangit, in the westdistrict of the state of Sikkim, India.The project is being developed byGIP’s wholly-owned subsidiary SikkimHydro Power Ventures Ltd (SHPVL).

In 2005, the same year it was incor-porated, SHPVL was awarded a build,own, operate and transfer (BOOT) con-

IPO to help fund Rangit II

In BriefPOOR WEATHER,limited materials suppliesand financial support havebeen given as key reasonsfor Iran being set to com-plete only 12 dams of the 18scheduled by the year-end of20 March. The Governmentsaid that the goal of com-pleting 18 dams in theIranian current year wouldnot be met, and added that ashortage of cement wasamong the reasons for fewerdams being completed.

MINING COMPANYNovaGold expects to havethe feasibility studies for theForrest Kerr hydropowerproject in British Columbiacompleted by mid-year. Therun-of-river scheme is beingdeveloped by subsidiaryNovaGreenPower, which isworking with HatchEnergy. To be built on theIskut river, the project couldhave an installed capacityof 195MW instead of theoriginally planned 115MW.

WILLIS GROUP Holdingshas been awarded a two-year contract to beinsurance consultant forthe operational assets ofthe Three Gorges project inChina. The plant on theYangtze river in Hubeiprovince will have 32700MW turbines. It isalready operational and isdue for completion by 2011.

CONSULTANT STUCKYhas won a contract todeliver dam analysisservices in the Caribbeanislands of Guadeloupe.The contract value isestimated at just overEuro22,100 (US$33,870)including VAT. Stucky wasawarded the competitivecontract by the ConseilGeneral de la Guadeloupe.

EDP output for PPAs hitby weak hydro in Q4-‘07

VA TechHydro winsbig orders

ENERGIAS DE PORTUGAL (EDP) SAWoutput down just over 39% to4,114GWh in the fourth quarter

of 2007 mainly due to low hydropow-er production. Hydro output for PPAsin Q4-’07 was down by two-thirdscompared to the previous period at1,431GWh from 4,334GWh. Loadfactor in the quarter was 16% versus48% last time.

But for the full year EDP’s outputfor PPAs decreased by 12.4% to18,295GWh with hydro only slightlydown on 2006. The hydro output lastyear was down 6.2% to 8,976GWh,and the load factor was 25% com-pared to 27% in 2006.

EDP’s installed hydro capacityincreased by 240MW to 910MW in

the liberalised electricity market inIberia, or almost a third of the totalincrease in 2007.

However, in the liberalised Iberianelectricity market, the Q4 output fromhydro was down almost 59% to216GWh. The load factor was 27%versus 35% in the previous period.For the full year the hydro output was12.7% lower at 1,171GWh, but theload factor increased to 35% from23%, said EDP.

EDP last year launched design workto increase the capacity of the Alquevaplant to 520MW, effectively double thepresent level. The utility also plans tobuild the Ribeiradio scheme in a JVafter the award of a concession by thenational water authority (Inag).

cession for Rangit II totalling 41 years,which includes six years of projectdevelopment (one year to achievefinancial closure and five years for con-struction) and 35 years of operation.

The concession was awarded bythe Government of Sikkim and theplant is due to begin operating inJanuary 2011. GIP has allocatedsums of Rs250M (US$6.2M) for eachof 2006-7 and 2007-8 to Rangit IIfrom the IPO proceeds. Its total equitycontribution is to be Rs1,300M(US$32.2M) over four years. The totalproject cost of the project is estimat-ed at Rs4,200M (US$104M).

WORLD NEWS


THE ASIAN DEVELOPMENT BANK(ADB) has put back its fundingassessment of the Song Bung 4

hydropower project in Vietnam by sixmonths. Originally scheduled for boardassessment last month, the banknow plans ro review the funding appli-cation in August. No reasons for therescheduling were given.

ADB is to assess an application fora loan of US$195M, already slightly

down from a previous request ofUS$196.5M. A grant of US$2M isalso sought for livelihood improve-ments for ethnic minority communitiesthat would be affected by the scheme.

The total project budget is esti-mated from feasibility studies atUS$254M, an increase on the esti-mate at the pre-feasibility stage ofabout US$220M.

The 156MW project is to have a

110m high RCC dam of 367m crestlength. A 3.1km long headracetunnel is to be excavated to feed thepowerhouse and the waters will bedischarged by tailrace canal to theriver, about 5km from the dam.

Song Bung 4 is to be built in theVu Gai-Thu Bon river basin in QuangNam province, near the border withLoa PDR. The reservoir surface areais to be 15.8km2.

ADB delays Song Bung 4 funds verdict

Kyoto effect for EU spotlighted in GHG reduction to ‘05

Idacorp ’07 results hitby weak hydrology

Rusal’s aluminium pact in China todraw on CPI group’s hydro

AltaGas buys four hydro prospects from Plutonic in BC

WEAK HYDROLOGY SET BACKIdacorp’s earnings last yearas costs increased and

more call was made on thermal pur-chases, but the US energy groupsees 2008 with potential better oper-ating conditions as it star ts with agood snow pack.

Last year, hydro generation wasdown by a third to 6,200GWh com-pared to 2006 but was within therevised estimate range given mid-year. Net income dropped just over23% to US$82.3M in the 12 monthsbut the relative fall was greater in thelast quarter – down 43% toUS$10.3M.

Difficulties were seen early in2007 as the year had started with apoor snow pack. During the year,retail demand also increased due tothe warm, dry weather. After the

THE HYDROPOWER RESOURCESof Huanghe HydropowerDevelopment Co are key to the

deal struck by its parent group ChinaPower Investment Corp (CPI) andRussian group Rusal for aluminium pro-duction in Qinghai province, China.

Rusal signed a memorandum ofunderstanding (MoU) with CPI to sup-port its plans to build a 500,000tonnes/year smelter in China. Aspart of a wider, international seriesof investments, the MoU gives Rusal49% of the smelter it will co-developwith CPI. CPI is to supply energy tothe smelter under the MoU from thehydropower plants on the Huang Heriver, and will fund the smelter in pro-portion to its ownership stake.

The companies plan to completean audit and a feasibility study by themiddle of this year and estimate thatthe joint venture scheme could com-mence construction in 2009.

ALTAGAS INCOME TRUST HASbought four run-of-river projectswith a combined capacity of

50MW from Plutonic Power Corp’sdevelopment pipeline in BritishColumbia.

In a statement, AltaGas said thatthe acquisition included all hydrologi-

GREENHOUSE GAS (GHG)emissions in the EU would havebeen 7% higher in 2005 with-

out initiatives implemented under theKyoto Protocol, according to a studyby the Netherlands EnvironmentalAssessment Agency (MNP).

However, to achieve the 2020target, the EU’s impact on carbondioxide reductions via new policies

The plant is to be operated as apeak load facility, which could seefluctuations in water level of up to1.5m near the station. Studies com-mencing in 2005, and the scheme isto be operational by 2011.

Loan proposals for the Song Bung2 and Song Bung 5 projects, to bebuilt on the same river, are not duefor decision by ADB until 2009 and2010, respectively.

second quarter the company hadnoted that it was experiencing ‘vastlydifferent’ water conditions comparedto the same period in 2006.

The continued weak hydrology overthe rest of the year ended the periodwith lower off system sales andhigher purchase power and fuelexpenses.

Looking ahead, Idacorp noted thatmid-February hydrological survey find-ings from the Snake River basin showsnow pack levels at 8% greater thanaverage. The US Weather Service’sNorthwest River Forecast Centerexpects higher – almost double –inflow to Brownlee reservoir overApril-July compared to the sameperiod last year, but Idacorp notedthat this would still be approximate-ly 16% less than the 30-year averagestream flow.

would have to increase by a factor ofalmost five, it added. For the widerGHG mix, the required reductionimpact is needed to increase by afactor of three, the agency concluded.

The new legislative package onenergy and climate in Europe is to bepresented in the coming months.

The study evaluated and quantifiedthe impact of environmental policies

on the emissions of the six GHGsunder the Protocol over 1990-2005,excluding the contribution of large-scale hydropower in the renewablesmix. Hydropower, though, will havecontributed to the actual benefit andincreasingly will do so.

The year of 2005 was taken as areference as it is the halfway mark inthe 30-year period between the start

in 1990 and the target year of 2020.The estimated 7% emissions

reduction equates to approximately370M tonnes of carbon dioxideequivalent.

The agency estimates that areduction of at least 1100M tonnesof carbon dioxide equivalent will beneeded as a direct consequence ofpolicies over 2006-2020.

cal and environmental data as well asengineering and permitting work gath-ered over the last four years for theprospective schemes, which range insize from 6.5MW to 24MW. In addi-tion, the sale includes water useapplications and land-use permits.

The projects include the planned

14MW Rainy River scheme nearGibson, which is at an advancedstage of development and should becommissioned in 2010, AltaGas said.

AltaGas issued Plutonic with con-vertible warrants in the acquisitionprocess. The firm already has175MW of renewable energy capaci-

ty under development or construction,including six run-of-river schemes.

Plutonic said it exited the RainyRiver and Hope-area prospects tofocus on its “green corridor” devel-opments in Toba, Bute and Knightinlets in the south west of theCanadian province.

CPI is building hydro assets on theHuang He river through its subsidiaryHuanghe Hydropower DevelopmentCo. The subsidiary itself has 13 affil-iated power companies, which includeplants, such as Bapanxia, Gongboxia,Laxiwa, Lijiaxia, Longyangxia,Qingtongxia and Yanguoxia.

The Gongboxia multi-purposescheme was built over 2001-06 andhas a total installed capacity of1.5GW (5 x 300MW) and produces5,140GWh per year.

The Longyangxia division develop-ing the Banduo hydropower project asthe first of 13 schemes with com-bined capacity of 8GW for theLongyang Gorge section of theYangtze river. The first unit of the360MW plant is to be commissionedat the end of 2010 and the schemeis due to be completed a year later.

The plant is to generate more than1,400GWh per year.

WORLD NEWS


In BriefPPL MONTANA IS TObuild a single unit power-house at Rainbow dam onthe Missouri river toreplace the present plant’seight units in a move thatwill almost doubleinstalled capacity to60MW. The company saidthe new powerhouse andsingle unit arrangementwas a fish-friendly design.Construction is to start inone year on the newpowerhouse, which will besited just downstream ofthe existing plant.

DROUGHT conditionshave forced Duke EnergyCarolinas to buy an optionto purchase 520MW moregenerating capacity and theUS utility has filed soughtto recover the extra costs ofgoing to the market byfiling for a rate hike.

MORE THAN 1.1M litresof water per second gushedfrom Glen Canyon Dam inthe US towards the GrandCanyon earlier this monthin a man-made flooddesigned to improve thelocal ecosystem. The delugewas said to be the equiva-lent of turning on 1.3Mgarden hoses simultaneous-ly. The flood will carrysedimentary residue toimprove the fish habitat inthe river and rebuildbeaches in the area.

GROWTH IN ITS INDIAoperations has enabledVoith Siemens Hydro toexpand its resources in themarket with a relocation ofthe main local office tolarger premises in NewDelhi. The business unithas 120 staff involved withincreasing volumes ofhydropower work, andthey are based in Noida.

OCEANLINX HAS SIGNED AMemorandum of Understand-ing (MoU) to supply power to

Maui in the Hawaiian Islands usingits wave power system.

The MoU was signed withRenewable Hawaii, Inc (RHI), whichis owned by the Hawaiian Electric Co(HECO). The state of Hawaii plans togenerate 20% of its electricity needsfrom renewable resources by 2020.

Three wave energy converters areto be installed offshore, north ofPauwela lighthouse on Maui, andsupply up to 2.7MW of power viasubsea cable into the grid operatedby Maui Electric Co.

Oceanlinx signs MoU for Maui as REHdeploys Ceto II wave energy prototype

BC Hydro’s output up in Q3,seeks capital funds for upgradeBC HYDRO REPORTED WATER

inflows higher than average inthe third quar ter to 31

December with consequent benefitsfor hydropower output and reducedmarket purchases to meet demand.In Q3, ‘07-’08, the inflows were114% of average rates.

Capital spend for the quarter wasCan$287M (US$288M), which was43% up on Q3 in the previous fiscalyear. BC Hydro said the expenditurewas higher due to preparations forthe winter season, refurbishmentand upgrades, transmission gridimprovement and work on the fifthturbine unit at Revelstoke.

In a statement, Alister Cowan,vice president and chief financialof ficer, said the spend hadincreased ‘significantly’ as BCHydro was focused on expandingdistribution and generation capaci-ty to meet rising demand asupgrade ageing assets nearing theend of their life.

The British Columbia utility hasfiled a request for authorisation of aCan$3.4B (US$3.4B) capital invest-ment programme for 2009 and2010. It is seeking a commensuraterate increase to also be approved bythe British Columbia UtilitiesCommission (BCUC).

Key improvement works to hydroassets planned for the periodinclude activities at: Peace Canyonplant; G.M. Shrum plant at W.A.C.Bennett dam; Mica plant; Aberfeldieplant; and, Coquitlam dam.

In addition, the fifth turbine to beinstalled at the Revelstoke plant isto have an installed capacity of500MW. The related budget for theproject is Can$280M-Can$350M(US$280M-US$350M), and theworks are to be completed in thefiscal year 2011-12.

At the Peace Canyon plant, theCan$141M (US$141M) package ofimprovements will include statorreplacement, rotor modification and

Third unit in operation at Svetlinskaya

THE THIRD OF FOUR GENERATIONunits at the Svetlinskaya(Vilyuiskaya GES-3) hydropower

plant has been commissioned tosupply electricity to Alrosa’s diamondmining operations in eastern Siberiaand other industrial operations.

Dmitry Medvedev, who wasRussia’s First Deputy Prime Minister

at the time, inaugurated the third unitat the power plant in Yakutia, saidAlrosa.

Construction of the project wasstar ted by the Soviet Union in1979, and it was not until late2004 that the first 90MW unit wascommissioned with Alrosa being theprimary investor.

The plant is to produce up to1200GWh annually and supply elec-tricity to the diamond mining andthe oil and gas activities in theYakutia region.

As a result, the energy costs inmining operations should bereduced, Medvedev was reported byInter-Tass to have said.

turbine overhaul. The works are to becompleted in the fiscal year 2010.

There will be a package of worksup to Can$91M (US$91M) related tothe stator replacement at Gordon MShrum plant. The works are to becompleted in the fiscal year 2010.

A stator replacement is alsoplanned for the Mica plant, and thebudget is Can$97M (US$97M). Theproject was initiated in fiscal year2007 and is due to be completed infiscal year 2010.

There is to be a package of seis-mic improvement works, budgeted atCan$66M (US$66M), for theCoquitlam dam, which was built in1913. The works are to be complet-ed in fiscal year 2009.

The Aberfeldie plant is being rede-veloped at a cost of Can$95M(US$95M). The project involvesupgrading the 5MW plant, which waspartly rebuilt in 1953, with a 24MWfacility. Completion is due in fiscalyear 2009.

The wave power technology isbased on an oscillating water columnthat drives air in and out of an airflowturbine. In a statement, Oceanlinxadded that it is negotiating with MauiElectric Co to sell power from thewave energy converter.

Meanwhile, Renewable EnergyHoldings (REH) has deployed andstarted initial operations with its CetoII wave energy prototype off the coastat Fremantle in Western Australia.

The company plans to have thetechnology for commercial roll-outnext year but before then will deploymore units at the test site for per-formance monitoring and further

design development.A full-scale Ceto III unit testing is

also planned for 2009.The Ceto system is sited on the

seabed and uses arrays of sub-merged buoys that move with thewaves and drive tethered pumps toconvey pressurised seawater toshore via a small bore pipeline.

The supplied water can either beused for power generation or reverseosmosis desalination, said the com-pany.

While developing the wave energytechnology, the London AIM-listed firmis also active in other renewableresources, such as wind power.


DIARY

Let IWP&DC’s readers know about your forthcoming conferences and events.For publication in a future issue, send your diary dates to: Carrieann Davies, IWP&DC, Progressive Media Markets Ltd, Progressive House,2 Maidstone Road, Foots Cray, Sidcup, Kent, DA14 5HZ, UK. Alternatively, email: [email protected], or fax:+44 208 269 7804

DIARY OF EVENTS

Power-Gen India & Central AsiaNew Delhi, India

CONTACT:PennWell Corp, Warlies ParkHouse, Horseshoe Hill, Upshire,Essex, UK, EN9 3SRTel: 44 1992 65 6600

9-11 AprilRoller Compacted ConcreteSeminar 2008Australia

CONTACT: RCC Seminar Events3 Plaxtol CourtAlexandra Hills QLD 4161AustraliaTel: +61 7 3206 3782Email: [email protected]

13-16 AprilUS National HydropowerAssociation Annual ConferenceWashington, USA

CONTACT: NationalHydropower Association, OneMassachusetts Ave., NW Suite 850Washington, DC 20001Tel: (816) 931-1311, ext. 108www.hydro.org

May 2008

21 May-22 May

June 2008

30 May - 2 June

1st International Conference onLong Time Effects and SeepageBehavior of DamsNanjing, China

CONTACT:Secretariat, Institute of HydraulicStructures, Hohai University, 1Xikang Road, Nanjing 210098,ChinaTel: +86 25 8378 6533Email: [email protected]://ltesbd08.hhu.edu.cn

2-6 June76th Annual Meeting of theInternational Commission on LargeDamsSofia, Bulgaria

CONTACT: CIM Ltd, 18 HristoBelchev Str, 1000 Sofia, BulgariaTel: +359 2 980 8961Email: [email protected]

11-13 JuneHidroenergia 2008Bled, Slovenia

CONTACT: European SmallHydropower Association (ESHA),Renewable Energy House, Rued'Arlon 63-65, B-1040 Brussels,BelgiumEmail: [email protected]

17-18 JuneWave Energy Summit 2008

CONTACT: First Conferences Ltd7-9 Fashion StreetLondonUnited KingdomE1 6PXTel: +44 (0)207 375 7218Email: [email protected]: http://www.firstconf.com/

24-26 JuneWorld Wind Energy ConferenceKingston, Canada

CONTACT: WWEACharles-de-Gaulle-Str. 553113 Bonn, GermanyTel.: +49 228 369 40 80www.wwindea.org

July 2008

2-3 July

FRIAR 2008 (InternationalConference on Flood RecoveryInnovation and Response)London, UK

CONTACT: Wessex Institute ofTechnology, Ashurst Lodge, Ashurst,Southampton, UK, SO40 7AATel: +44 238 029 3223Email: [email protected].

13-16 JulyICEFA III Conference onEngineering Failure Analysis)Barcelona, Spain

CONTACT: ConferenceSecretariat, ICEFA III, 51 KestrelWay, Wokingham, Berkshire, UK,RG41 3HATel: +44 118 977 6680Email: [email protected]

14-18 JulyHydroVision 2008Sacramento, California, US

CONTACT: HCI Publications, 410Archibald Street, Kansas City, MO64111, USATel: +1 816 931 1311Email: [email protected]

April 2008

3-5 April

September 2008

7-11 September

Dam Safety 2008California, US

CONTACT:Sarah Mayfield, Association ofState Dam Safety Officials, 450 OldVine Street, Lexington,KY 40507, USTel: +1 859 2575140Email: [email protected]

8-12 September8th International Conference onHydroscience and EngineeringNagoya, Japan

CONTACT: ICHE ConferenceSecretariat, Nagoya University,Department of Civil Engineering,

Furo-cho, Chikusa-ku, Nagoya,Aichi 464-8603, JapanTel: +81 52789 4625www.civil.nagoya-u.ac.jp

22-27 SeptemberWorld Tunnel Congress 2008New Delhi, India

CONTACT: Mr G N Mathur,Congress Secretariat, Central Boardof Irrigation and Power, CBIPBuilding, Plot no 4, InstitutionalArea, Malcha Marg, Chanakyapuri,New Delhi - 110021, IndiaTel: +91 11 26115984Email: [email protected]

October 2008

12-17 October

14th World Conference onEarthquake EngineeringBeijing, China

CONTACT:Conference Secretariat, ChineseAssociation of EarthquakeEngineering, 9 Xuefu Road, Harbin150080, ChinaTel: +86 451 8665 2900Email: [email protected]

13-19 October20th International Congress onIrrigation and DrainageLahore, Pakistan

CONTACT: Syed Raghib AbbasShah, Conference Secretariat,Organising Committee, 506WAPDA House, Lahore, PakistanTel: +92 429202538Email: [email protected]

22-24 OctoberCentral European Power Show 2008Krakow, PolandLahore, Pakistan

CONTACT:Syed Raghib Abbas Shah,Conference Secretariat, OrganisingCommittee, 506 WAPDA House,Lahore, PakistanTel: +92 429202538Email: [email protected]

All-Energy '08 Exhibition &ConferenceAberdeen, Scotland, UK

CONTACT: Media GenerationEvents Ltd, 34 Ellerker GardensRichmond, Surrey,TW10 6AA,United KingdomTel: +44 20 8241 1912Email: [email protected]

30 May-2 June1st International Conference onLong Time Effects and SeepageBehavior of DamsNanjing, China

CONTACT: SecretariatTel: +86 25 8378 6533Email: [email protected]

Submit your tenders to us, here at IWP&DC, free of charge, for publication in a future issue.Send approximately 200 words, with a contact name and contact details to: Progressive Media Markets Ltd, Progressive House, 2 Maidstone Road,

Foots Cray, Sidcup, Kent, DA14 5HZ, UK. Alternatively, email tenders to [email protected] or fax:+44 208 269 7804

CALL FOR TENDERS

USConsultant hired

FijiCivil works invitation

Fiji Electric Authority (FEA) hasinvited bids for the constructionof the civil works of theNadarivatu hydropower project.Brief descriptions of the works areas follows:• Establishment and operation of

a construction camp.• Construction of a weir on the

Sigatoka river. The weir willconsist of:– Concrete gravity weir struc-

ture.– Three radial spillway gates.– Two low level sluice gates.– A single residual flow con-

trol valve.– Control building and appur-

tenant facilities.• Nadarivatu Water Conveyance

System.This will consist of:

– an intake structure compris-ing screens, intake gate, stoplogs and screen cleaner.

• Either:– Conveyance option 1:

“Tunnel-Tunnel”; or– Conveyance option 2:

“Tunnel-Penstock”.• Project-wide roads (excluding

transmission line road only) andmaintenance of public roadsthroughout the project duration– and other works described inthe bid documents and relatedproject drawings.

CONTACT:www.evalua.com.au/fea

IndiaFunds for small hydro

AfghanistanContract agreement signed

BotswanaExpressions of interest

CanadaContracts won

The deadline for the engineering,procurement and construction(EPC) package of civil works andhydromechanical equipmentworks for the Vishnugad Pipalkotihydroelectric project has beenrescheduled to 27 March. Theoriginal deadline was 27 February.

Civil works include:

Afghanistan’s Energy and WaterMinistry has signed a US$2Mcontract with an Iranian firm toconduct preliminary studies onthe construction of the 120MWGol Bahar dam on the Panj Shirriver in northern Afghanistan.The scope of work includes eco-logical and terrestrial studies, aswell as assessing the technical fea-sibility of constructing the dam.According to the Afghan Ministryof Water and Energy, the countryhas the potential to develop asmuch as 12,000MW of electricity.Afghanistan intends to construct30 dams to produce part of theneeded hydroelectricity using them.The country generates 400MW ofelectricity currently and buys500MW from Iran, Turkmenistan,Uzbekistan and Tajikistan.

Gaborone, Botswana-basedWestern Power CorridorCompany (Westcor) has called forexpressions of interest from vari-ous disciplines for servicesrequired to construct the4,300MW Inga III hydro project.Inga III is to be developed by fiveutilities in Angola, Botswana, DRCongo, Namibia, and SouthAfrica. Westcor is a joint ventureof Nampower (Namibia), Eskom(South Africa), ENE - EmpresaNacional De Electricidade(Angola), SNEL of Congo and theBotswana Power Corporation.Each utility owns 20% of theshare capital of Westcor. The pre-feasibility study for the baseloadhydro station was completed latelast year. It is expected that con-struction would start in about 18-24 months. Westcor has called forexpressions of interest for theappointment of legal advisors,recruitment of advisors, consul-tants and front line office opera-tion staff to be involved in whatwould be the largest single powerstation in Africa. The organisa-tion is also calling for expressionsof interest for power system eco-nomic advisors, financial advisors,engineering consultants, environ-mental impact assessment con-tractors, risk managementadvisors, project managers andquantity surveyors, as well as full-time employment, to be taken upin Gabarone in Botswana.

St. Johns, Newfoundland-basedengineering company Rutter, Inc.has announced that its controlsand automation division has wona Can$2.9M (US$2.93M) con-tract for electrical engineering ser-vices and control systems for ahydro power project in BritishColumbia. Rutter said its RutterHinz, Inc. division will providethe services for the proposedhydroelectric project at the head-waters of the Toba Inlet in BritishColumbia. The Rutter Hinz divi-sion has offices across Canadaand operations in the UnitedStates and Brazil.Meanwhile, Toronto-based AdexMining has awarded the contractfor repairing and upgrading thetailings containment area at itsMount Pleasant project in NewBrunswick to MonteithUnderground Services ofFredericton. Mount Pleasant is aformer tungsten producer devel-oped and operated by BillitonExploration in the mid-1980s.The work to be done includesstructural repairs to the existingtailings dam, the installation of anew emergency spillway, andupgrades to the existing decantstructure. The work is to begin in


The Escondido City Council inCalifornia has approved aUS$196,000 contract withCarlsbad-based GEI Consultantsto study the Lake Wohlford’s damto determine how to reinforce itso that it can withstand a majorearthquake. Wohlford rock damwas built in 1895, reaching aheight of just over 23m.The concern is that portions ofthe dam added later could lique-fy in a major quake, causing it tofail. Most of the water in the lakenortheast of Escondido comesfrom Lake Henshaw and is chan-nelled through the EscondidoCanal.The lake is a source of water forthe cities of Escondido and Vista.In 1924, authorities added 7.4mto the height of the dam using siltand sand and reinforced the land-ward side with similar materials.

TENDERS

early June and be completed bylate August. It will bring the facil-ity up to current standards foroperation.

– 65m high gravity concretedam;– 10m diameter diversion andspill tunnel.– 12m diameter spill tunnel.– Intake structure followed bythree desilting chambers (each350m long by 16m wide by20.6m high).– 13.4 km long by 8.8m diam-eter horse shoe-shaped head-race tunnel.– 130m high by 22m diametersurge shaft.– 351m long by 5.2m diameterpressure shaft.– Underground powerhouse forfour vertical Francis turbinegenerating each 111MW.– Underground transformer

cavern.– 120m long by 12m wide by

27m high underground surgetank.

– 3.07km long by 8.8m diame-ter horse shoe-shaped tailracetunnel, a cofferdam, etc.

CONTACT: Tehri HydroDevelopment Corporation,Ganga Bhawan, Bypass Road,Pragatipuram, Rishikesh 249201,Uttarakhand.Tel. +91 1352430721

But the materials were not prop-erly placed.Although the dam passed statetests in the intervening years, theintegrity of the sand-and-silt con-struction is suspect when sub-jected to a Richter 7.5 magnitudeearthquake loading.Since then, the Escondido haskept Lake Wohlford at half-capacity. The level of the reser-voir is kept below the height ofthe original rock dam, which wasshown in the federal tests to bestrong enough to withstand earth-quakes and floods.The consultant’s report should becompleted by July.

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INSIGHT

CDC backsCameroon projectDevelopment proposals for hydropower projects, such asMemve’ele, are advancing in Cameroon, reports Neil Ford

CENTRAL AFRICA possesses hugeuntapped hydroelectric potentialthat could be developed for thebenefit of the region and the wider

continent. The required investment hasbeen less than forthcoming, partly becauseof intense conflict in the Congo Basin andelsewhere, but also because local powerutilities lack the financial muscle to fund

dam construction. International firms havebeen unwilling to invest in power genera-tion of any kind in most parts of Africa.However, a new kind of power sector com-pany has now agreed to develop a hydroscheme in Cameroon that could encouragefurther investment across the region.

The 200MW Memve’ele hydro projectin the southern provincial district of Ma’an

of Cameroon, close to the border ofEquatorial Guinea, is to be developed bythe UK’s CDC Group (formerly known asthe Commonwealth DevelopmentCorporation). When the project was orig-inally agreed with the Government ofCameroon, it was signed by CDC offshootGlobeleq, but responsibility for managingMemve’ele is now in the process of being

THE CAMEROON PWER SECTOR

Unlike in many other African states, aninternational power company is alreadyheavily involved in the Cameroonian powersector. US company AES Corporation tooka majority, 56%, stake in power utilitySociété Nationale d’Electricité deCameroon (SONEL) in 2001, leaving theGovernment of Cameroon with the remain-ing 44% equity. Through its AES SONELoffshoot, AES currently controls the entirepower sector from generation through totransmission and distribution. The rate ofelectrification is higher than in most othercountries in the region and power is nowsupplied to 500,000 homes.

At present, the main thermal power plantis the 85MW Limbé facility, which relies onexpensive oil feedstock and which is gener-ally used as back up generation during thedry season and prolonged droughts.Although Cameroon possesses significantbut scattered associated gas reserves on itsestablished oil fields, the government hashad little success in attracting foreigninvestment in gas to power projects. As aresult, the country continues to rely on thehydro sector to provide 87% of all powerproduction. The 384MW Song Loulou and263MW Edea hydroelectric projects, bothlocated on the Sanaga river, are still thelargest hydro schemes in Cameroon, asdevelopment plans for Lom Pangar,Memve’ele and Nachtigal dams have beenrepeatedly delayed.

AES SONEL requires access to greatergenerating capacity, either from its own

passed to the Government of Cameroon.Providing the preliminary studies proceedas planned, construction is scheduled tobegin in 2009, with the first electricity duein 2013.

An operating concession will be award-ed once CDC has completed its preliminarycommercial and technical studies, and thegovernment has concluded the variousenvironmental and social impact assess-ments. The government will also be respon-sible for feasibility studies on access roadsand the transmission line. Whether or nota concession is awarded, the frameworkagreement will expire in two years. CDChas not put a figure on the total cost of theproject but a government official suggestedin 2005 that it could be CFA Franc 142B(approximately US$330M).

Cameroonian officials said 50MW ofMemve’ele’s capacity will be used tosupply the Alucam smelter, while a further20MW will be dedicated to rubber com-pany Hevecam. It has also been suggestedthat Equatorial Guinea will sign up toanother 50MW of capacity, with Gabona further potential customer. Cameroon’sMinister of Finance, Polycarpe AbahAbah, commented: ‘This project is reallyimportant for the economy of our coun-try. You know that we are facing seriousenergy problems every day. On a dailybasis, it affects our industries, our enter-prises and household use. That is why Ithink the signing of this convention is agiant step in resolving this energy crisisthat very negatively impacts our econom-ic growth.’

transferred from Globeleq to ActisInfrastructural Fund. Actis, which willmanage the venture on behalf of CDC, is aprivate equity company that specialises inemerging markets. CDC aims to invest ininfrastructural projects in developing coun-tries that are commercially attractive butwhich also boost the living standards ofpeople living in some of the world’s poor-est countries. CDC had previously con-centrated on investing in thermal powerplants in Africa, Asia and Latin Americabut in August and November last year itsigned agreements with the Government ofCameroon to develop the Memve’elehydro scheme on the Ntem river.

The 200MW of generating capacity willprovide a significant boost to a powersector that currently relies on just 902MWof capacity. A new transmission line will beneeded to link the national grid to the site.The preliminary technical studies for theproject are to be undertaken this year butno further project details are available atpresent. Details of the dam and turbines tobe developed on the river Ntem have notyet been released.

CDC will provide 30% of developmentcosts, the remainder supplied by theAfrican Development Bank (AfDB), theDevelopment Bank of Central AfricanStates, the Dutch Development Bank, theArab Development Bank and theMultilateral Investment Guarantee Agency(MIGA), a member of the World BankGroup. The hydro scheme will be devel-oped under a build, operate, transfer (BOT)contract, after which the asset will be

INSIGHT

NIGERIA

CAMEROON

GABON

EQUATORIALGUINEA

DEMOCRATIC REPUBLICOF CONGO

CENTRAL AFRICANREPUBLIC

Memve’eleProject

Site Bata

Douala Yaoundé

Ebolowa

Libreville

Port Gentil

Mbalmayo

Bertoua

Bamenda

Limbe

CalabarAba

Warri

EnuguBenin CityLagos

Ibadan

PortHarcourt

MalaboAbongMbang

Figure 1 – Location map of the proposed Memve’ele hydropower project in Cameroon



INSIGHT

plants or independent power producers(IPPs), if it is to continue with its rural elec-trification programme, and supplyincreased industrial capacity. Much of thecompany’s budget for 2005-09 is dedicat-ed to improving downstream infrastruc-ture, so it is likely that much of anyadditional generating capacity will be pro-vided by other investors.

One of the power utility’s main aims is toincrease the size of its customer base overthe next decade and beyond, partly byextending its regional power grids to partsof the country that were previouslyunserved.

This expansion programme, includingthe addition of 50,000 new connectionsevery year for the next 14 years, has nowbeen included in the contract AES SONELholds with the government and so must beimplemented through the commissioning ofnew generating capacity. In 2006, the firmsecured a US$405M loan from the WorldBank’s International Finance Corporation(IFC) to fund its transmission and distrib-ution projects, one of the biggest loans everawarded to a privately owned power com-pany in Africa.

Additional funding has been provided bythe European Investment Bank (EIB),AfDB, the Central African DevelopmentBank, Deutsche Investitions undEntwicklungsgesellschaft (DEG), theEmerging Africa Infrastructure Fund, theNetherlands Development FinanceCompany, and Proparco.

John McLaren, the president of AESEurope, CIS and Africa, said: “This is themost ambitious expansion programme forCameroon’s electricity sector. We expect tomore than double the number of people weserve in Cameroon and to provide electric-ity to thousands of individuals who neverhad it before. AES SONEL is committed toimproving Cameroon’s energy sector, whichis essential to the country’s continued eco-nomic development and we’re pleased tomove forward with the government under

our amended concession agreement.”Demand for electricity is currently grow-

ing by about 8% a year and the govern-ment has set a target of more than doublingnational capacity to 2,000MW by 2015.The completion of Memve’ele would be astart but the government is eager to ensurethat Lom Pangar and Nachtigal are alsodeveloped. This goal is achievable but onlyif all the projects currently in the pipelineare actually developed. While Cameroonhas one of the most diverse economies inCentral or West Africa, with a significantmanufacturing sector, the lack of powergenerating capacity has indeed held up eco-nomic growth for many years.

A new interconnector betweenCameroon and Chad has been proposedthat would allow Cameroonian hydroschemes to export electricity to its neigh-bour. Although Chad has traditionally beenone of the least developed countries in theworld and is currently suffering from severepolitical instability, its economy is expand-ing rapidly as a result of its new oil indus-try and the Chad-Cameroon oil pipeline. Asa result, the country is now in a somewhatbetter position to import electricity thanpreviously.

ALUMINIUM SECTOR DEMAND

However, it is domestic industrial con-sumption that is likely to provide the mainmarket for any new hydro projects.Aluminium company Alucam alreadyabsorbs almost 45% of total electricity pro-duction at its Edea smelter but plans toboost output at the plant from 90,000tonnes per year to 300,000 tonnes per yearwere held up by the lack of new power gen-erating capacity. Alcan of Canada (nowpart of Rio Tinto) and the Government ofCameroon had both held 46.7% stakes inAlucam and both had hoped that the LomPangar and Nachtigal schemes, whichwould also be developed on the Sanagariver, could be developed to supply elec-

tricity to the smelter.However, Rio Tinto has adopted a new

approach since it took over Alcan inNovember 2007. Two weeks after theAlcan acquisition has been completed, thenew firm of Rio Tinto Alcan announcedthat it had signed a preliminary develop-ment agreement with the Government ofCameroon for the development of a1,000MW hydro scheme at Songmbenguéthat will provide both power and water fora new green field aluminium smelter withproduction capacity of 400,000 tonnes peryear.

Technical and pre-feasibility studies forboth the smelter and the power plant willnow be undertaken, with the final invest-ment decision expected by the end of 2009.

The chief executive and president of RioTinto Alcan Primary Metal, Jacynthe Coté,said: ‘What we are seeing today are theresults of the long and prosperous collabo-ration between Rio Tinto Alcan and theGovernment of Cameroon. This is apromising project that will have a positiveimpact for all stakeholders.’

However, investigating the Songmbenguéscheme does not mean that the Lom Pangarand Nachtigal ventures will be abandoned.All technical studies and the environmentalimpact assessment on the construction of a330MW hydro plant at Nachtigal to supplythe existing Edea smelter have now beencompleted. As a result, Rio Tinto Alcan isnow negotiating the terms of a power pur-chase agreement (PPA) with AES SONEL,which is expected to operate Nachtigal.

In addition, Rio Tinto Alcan and the gov-ernment have agreed to discuss how tospeed up the construction of the LomPangar project. Not all of the electricityfrom the three schemes would be used tosupply aluminium smelters; a large pro-portion could be made available for widerdistribution by AES SONEL. US miningcompany Geovic has also discussed devel-oping cobalt reserves in the south east ofthe country and it, too, would require sub-stantial electricity supplies.

The environmental impact assessment onthe Lom Pangar project, which would belocated 4km downstream of the confluenceof the Lom and Pangar rivers, is nowunderway. Figures for the expected gener-ating capacity of the scheme vary but thegovernment predicts that the dam wouldhelp to boost generating capacity at theexisting Song Loulou and Edea hydro pro-jects by between 105MW and 216MWduring droughts.

However, the World Bank is concernedthat the new dam could have an impact onthe Chad-Cameroon oil pipeline, as thereservoir will submerge part of the pipeline.There are also fears about the impact onlocal farm land and on the Deng DengForest Reserve, which is home to an impor-tant gorilla population. There is also exten-sive tropical hardwood forest that wouldbe flooded.

Hydromechanical equipment

10%

Civils works36%

Electromechanical equipment

28%

Engineering &administration

8%

Contingency17%

Figure 2 – Anticipated breakdown of works at Memve’ele

Source: Coyne et Billier - Memveʼele, Actualisation des Etudes de Faisabilite, Note de Synthese. Feb 2006


INSIGHT

CDC STRATEGY

Yet, while Cameroon’s potential as an alu-minium producer has long been recognised,it has taken a company with developmentpriorities to finally put pen to paper on thefirst new hydro scheme. The British firm’sstrategy could herald similar ventures else-where in the developing world. CDC hasrecently sold generating assets in NorthAfrica, Asia and Latin America, and soappears to be focusing solely on Sub-Saharan Africa. A company spokespersonsaid that after last year’s sales, it still had adiverse portfolio of developments, with1,500MW of generating capacity includingthe 200MW Memve’ele project. Divestingitself of power plants after just a few yearsof operation could be part of the company’sstrategy, as it seeks to ensure the success ofeach project before handing over the reins.

CDC’s other generation projects in Africa

larly in developing countries, are becomingmore acceptable. Historically, the advan-tages in terms of development have oftenbeen outweighed by the environmentaldamage, but the additional benefits of lowcarbon power generation could now makehydro more attractive to the multilateralsand a number of potential investors.

While the World Bank had tightened thecriteria for supporting large hydro in thewake of the World Commission on Dams(WCD) report, it now seems more enthusias-tic about hydroelectric ventures that promotedevelopment and help to tackle climatechange. In April last year, it completed its pro-gramme of economic, environmental, andsocial due diligence on the long-delayedBujagali hydro scheme in Uganda and its sub-sequent financial backing gave the green lightto a procession of banks to do likewise.Construction of the project began last year,and the electromechanical contract wasrecently awarded. The plant is due to be oper-ational in 2011. The World Bank lendingguidelines are followed by many other fund-ing organisations and some privately-ownedcompanies, such as CDC, so the multilateralsslight change of approach seems to be havinga far greater impact than might be expectedfrom its own limited investment funds.

CDC chief executive, Richard Laing, saysthat his company’s existing US$2B in assetswill enable it to expand its operations. Hecommented: ‘We will now use this as a plat-form to invest more in power generation inAfrica. Many countries in Africa have min-eral wealth, high economic growth, and theadditional attraction of consumers in theregion now experiencing, for the first time,a higher amount of disposable income.Africa has caught people’s imagination.’Laing said that India and China were stillgenerating the best financial returns butadded that interest in Africa was increas-ing, particularly among more mainstreamprivate equity companies. He concluded:‘Firms like CDC, however, are still neededto fill some of the investment gaps particu-larly in relation to funding for small andmedium sized enterprises.’

Given the reluctance of many other inter-national investors to dip a toe in Africanwaters, CDC’s strategy of focusing onemerging markets power projects that arecommercially driven but which also bringsignificant benefits in terms of developmentcould be a model for more general powersector investment in Sub-Saharan Africa.Coupled with Chinese investment inGhana’s Bui hydro scheme, new sources offinancial support do appear to be emergingbut it is certainly interesting that a develop-ment-led power company has opted forhydro in the case of Cameroon. Whether thecompany pursues this policy in other Africanstates remains to be seen, but if CDCbelieves that Memve’ele can be profitable,there are dozens of similar undeveloped sitesacross Central Africa that could be exploit-ed by private sector investors. IWP& DC

CHAD

CAMEROON

GABONEQUATORIALGUINEA

CENTRAL AFRICANREPUBLIC

DEMOCRATIC REPUBLICOF CONGO

Mbakaou dam & reservoir

Mape dam& reservoir

Lom-Pangarproject

Nachtigal Project

Song-Loulouhydropower plantInstalled capacity:384MWOutput (2003): 1.878GWh

Bamendjin dam& reservoir

Lake Tchad

Sanaga

Edea hydro plantinstalled capacity: 257MWOutput (2003): 1.453GWh

DoualaYaounde

Memve’ele hydropower projectInstalled capacity: 200MWOutput: 1.140GWh/an

NTEM

75 150km0

AtlanticOcean

NIGERIA

Figure 3 – xxxxx

are the Azito Energie 288MW gas firedplant in Cote d’Ivoire; the Sidi Krir685MW gas fired facility in Egypt; theTsavo Power 74MW fuel oil thermal plantin Kenya; the 180MW gas fired plant inTanzania; and South Africa’s 600MWKelvin coal-fired facility; so it is interestingthat Memve’ele is its first hydro scheme.When asked whether his company had anew found interest in hydro, the CDCspokesperson said that the company ‘hasalways evaluated each project based on itscharacteristics and the characteristics of themarket it will serve; our work onMemve’ele reflects that. When consideringthe development of a new power plant, weevaluate all of the practical alternatives andare guided by what makes the most sense,in terms of technology, size and commercialterms, for the market we wish to serve’.

However, it is difficult to escape conclud-ing that some large hydro projects, particu-

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RCC

Myanmar, and the Son La scheme on the Da river in Vietnam.Yeywa is Myanmar’s first RCC dam. The scheme comprises a

134m high RCC gravity dam with a total volume of 2.5M m3 ofconcrete. Other features include an ungated spillway for a designflood of 6,600m3/s and a 790MW (4 x 197MW) powerhouse atthe toe of the dam on the left bank.

The 2,400MW Son La project is under construction approxi-mately 360km north west of Hanoi. It is a 138m high structurewith RCC volume of approximately 3.1M m3 (total volume is4.6M m3), with a peripheral spillway with a capacity of35,000m3/s. Located on the right bank, the spillway has eightgates in addition to 16 low level gates to control water levelsduring the flood season.

Son La is considered to be of national importance and willsupply 9GWh annually to the grid. River regulation will alsoenable the 1980MW Hoa Binh plant, which is downstream, tooperate fully. Son La is the second of four dams to be built on theriver and is an integral part of the largest hydropower project cur-rently under construction in south east Asia. Upon completion the

As RCC dam construction is centred upon a sequence ofhighly mechanised activities, the key to successful deliv-ery of a fast yet high quality and economical project is asimple design that facilitates a smooth construction

process. Two interesting RCC dam projects achieving excellentprogress are under construction in south east Asia - the Yeywahydropower project, located on the Myitnge river in central

Speedy construction is a pre-requisite for RCCs in tropical climates and two projects insouth east Asia are making good progress. Report by Suzanne Pritchard

Left: Artist’s impression of Son La hydropower project in Vietnam

Below: View, from left abutement, of RCC placement work getting underwayat Son La, in January


RCC

whole scheme will have an installed capacity of 6,532MW and willprovide flood control, water supply and regulation.

PREFERRED CHOICE

Compared with conventional gravity and concrete face rockfilldams (CFRDs), RCC dams are generally the preferred choice ofdesigners when working in the tropical conditions experienced insouth east Asia, especially as the dry season can last only about sixmonths. The effective scheduling of construction sequencesinvolved with the RCC process helps to facilitate continuousprogress, which is particularly advantageous during the wet seasonas it can reduce the cost of the river diversion. It can also reducetimescales and the cost of the project as a whole. The arrangementsthat facilitate such economies for the project are:

* Integrated Cofferdam: Construction of an integrated cofferdamas part of the main cross-section enables downstream constructionworks at a later stage.

* Intentional overtopping: The purposeful overtopping of RCCsections located in the river section, and continued RCC placementin the dam portions protected against floods.Both of the above arrangements contribute to smaller diversiontunnels or culverts to secure the construction site against floods inthe wet seasons, which help to reduce project costs. At Yeywa, alongitudinal separation wall (needed to separate the tailrace chan-nel from the spillway) was constructed between the overtoppingsections and left bank sections, which allowed for continued place-ment of RCC at the left bank during the wet seasons. At Son La,the same task is fulfilled by the diversion culverts.

The advantages of selecting RCC were seen at Yeywa, where somemajor setbacks have been experienced during construction. The mostserious was in October 2006 with the occurrence of a 1:50 year floodat the end of the rainy season. The project’s integrated RCC coffer-dam arrangement protected the downstream works in the river sec-tion against the floods. The 60m high cofferdam was designed forfloods with return periods of 1:50 years.

The construction works themselves have remained relativelyfree from the major damage that can be caused by such occur-rences, although there has been some delay. The intentional over-topping of the RCC sections already constructed in the riversection can take place at the same time as continuing with RCCconstruction on the left bank section. Such a major flood securi-ty advantage is not to be underestimated, especially in countrieswhere extreme power shortages combined with frequent short-ages of fuel and pumping capacities are prevalent. It is argued,

therefore, that this proves an advantage of RCC in relation toCFRD and rock fill methods of construction.

Construction of Son La dam is on a tight schedule, though,because of the need to improve flood control on the Da river. Thesignificant number of flood events that occur each year during thewet season means that river diversions must be able to handle largefloods. The floods in 2007 wet season reached some 12,000m3/swhile in the previous year the flow rate reached even higher, atapproximately 15,000m3/s.

INTEGRATED PLANNING

An integrated plan is required early in the design process to helpensure the greatest opportunity to reap the full economic and qual-ity benefits associated with a well-designed RCC dam. The planmust ensure that the sourcing, transportation, production and plac-ing of the RCC can run smoothly, especially in the rainy seasonand when confronted by significant flooding. Other factors thatneed to be considered include the appropriate selection of con-struction methods and equipment for RCC transportation to, andapplication at, the dam.

As with any construction endevour, ensuring uninterrupted paceof construction is vital and so disruptive activities or structuralinterfaces have to be a minimised, possibly moreso for RCC dams.From a design point of view, this means that structures that wouldintercept the linear progress of the RCC equipment on the place-ment area must be kept to a minimum, if not banned. Such struc-tures include: galleries, which should be reduced in number to onlythe essential; transverse galleries which connect inspection gal-leries but should be eliminated; and, likewise, vertical shafts (suchas staircases and elevators) or other large chambers in the RCC

Production and placement atYeywa – the factsCrushing plants – Operating using a dry process; three have been installedwith a similar arrangement of a primary jaw crusher, a secondary impact orcone crusher and a vertical shaft impact crusher. The specified productionrate is 150,000 tonnes per month. The aggregate stockpile is 1M tonnes.

Concrete plant – the aggregate stockpile here is 50,000 tonnes. Afterdelivery to the plant the coarse aggregate is cooled to 10ºC in a 150m longcooling gallery. It is then conveyed to the inline silo above the batchingplants. The concrete plant consists of four, twin-shaft batch mixers with atheoretical peak production of 4 x 125m3/hr. The practical output achievedfor each plant with the conditions at Yeywa has been 110m3/hr. Below thefour mixers a special delivery system has been designed to allow dischargeof the mixer either to trucks, or to a reclaim conveyor that feed the RCC at acontinuous rate to the high-speed conveyor system. In total 6,500 tonnes ofnatural pozzolan and 3,500 tonnes of cement are kept in steel silos.

Delivery system – A high speed conveyor system runs at a design speed of4m/s. The conveyor is supported on self-raising posts that are adjusted inheight with the progress of the dam construction stages. A swinger conveyorloads the continuous flow of concrete onto the dump trucks. In some stagesof the construction steel chutes at 45º inclination and with a maximumvertical height of 35m have also been used for the delivery of concrete to theplacement area.

The system has been used successfully in China when operated with asimilar type of RCC mix that is rather cohesive and does not segregate.

Concrete placement – RCC spreading is carried out with Caterpillar D5 typelaser-guided dozers and compacted with 10.5 tonnes static weight vibratoryrollers. A large amount of paste is brought up to the lift surface duringcompaction and has been designed with a high retardation (initial set of themix is 20hr). A uniform and permanent water curing of the exposed surfacesguarantees that the surface layer is still fresh when the next layer is placedon top. Very good tensile strength across the lift joints (the critical designparameter) has been achieved without the need for any treatment or beddingmixes placed between RCC layers.

Above: Full scale trial embankment No.2 at Son La RCC dam site withpreparations ongoing for placement of a new layer in the rainy season


RCC

sections should be eliminated. Where such structures cannot beavoided, the placement area can be increased to develop the fulleffect of the high degree of mechanisation involved in the RCCplacement process.

At Yeywa, the power intake towers were designed as convention-al reinforced concrete structures abutting onto the upstream face ofthe RCC dam. This enabled the contractor to build the four towersabove the penstock inlets before the start of RCC construction.

This not only helped to minimise effects on RCC constructionactivities, but has also enabled the Department of Hydropower inMyanmar to construct these above the inlet bellmouths and closedgate positions in advance. Such methods have helped to avoid sig-nificant delays.

ALL IN THE MIX

The desired high quality of RCC dams depends on accelerated ratesof construction. The speed at which RCC is placed has a greatinfluence on the quality of the horizontal lift joints, ie the bondbetween the 300mm thick RCC layers in the dam to ensure thatthe tensile strength and seepage across the horizontal lift joints areeffectively identical to that of the parent RCC itself.

The mix design methodology is based on a high-cementitiousapproach, which enables the delivery of construction speed, lift jointquality and thereby simplified targets. The total cementitious con-tentof the mix, cement plus pozzolan, will not be less than 150kg/m3

of RCC. Admixtures are used to help retard the set time up to 24hours, and enables fresh concrete bonding between layers.

High-cementitious RCC mixes with a high volume of pozzolan asa cement replacement is considered to be the norm for the majorityof large RCC dams. Pozzolan can be obtained from natural sourcessuch as volcanic or fly ash from the by-products thermal power plants.Good pozzolan contributes to the strength of the RCC mix and insitulift joint properties, which enables further cement replacement andmore favourable thermal conditions - maintaining hot joints reducesthe need for time-consuming joint preparations at a later stage.

Locally sourced pozzolans offer significant cost benefits to pro-jects. The search for suitable pozzolans for Son La dam resulted inthe use of fly ash from the Pha Lai thermal power station, some425km from the construction site. The pozzolans were a more effec-tive cementitious material than Portland cement. Consequently,mix design trials indicated that a total cementitious content of220kg/m3, comprising 60kg of cement and 160kg of fly ash, wouldproduce the necessary characteristics for a good quality RCC dam.In addition, three full-scale trial embankments were constructed.

Fly ash, which contains a large proportion of unburnt carbon, canresult in a higher LoI value which can have an effect on the strength anddurability of the RCC structure. Therefore, the last of the three trialswas undertaken not only for training purposes but also to prove thatfly ash with a loss of ignition (LoI) value in the upper limit does not havea detrimental effect on RCC performance. LoI values for the fly ashfrom Pha Lai thermal power station were up to 25% but the third trialembankment used an RCC mix containing fly ash with a LoI of 12%.

Son La scheduleMarch 2005 – Construction of the project started with excavation of the 90mwide diversion tunnel and two 12m by 12m dry season culverts, plusexcavation of the abutments.

December 2005 – River closure ceremony took place with subsequentexcavation to the dam foundation level in the river channel.

2007 – Foundation treatment and levelling of concrete.

January 2008 – RCC placement started.

October 2012 – Project scheduled for completion.

Above: Yeywa RCC dam under construction in Myanmar, in January

Left: Earlier works at Yeywa showing, left, overtopping of Stage 1 and 2 (July2006), and, right, before completion of integrated cofferdam (April 2007)


RCC

LoI values from Pha Lai varied from a high of 30% to a low of6% over a year, the use of ash with a LoI greater than 12% hasnever officially been recorded. Vietnamese regulations view thelower limit of 6% LoI as the appropriate standard to be used, eventhough 12% is permissible if sufficient tests have been carried out.The trial mix tests have shown that there is little difference in thestrength and durability results after three years even with LoIvalues up to 20%. However, without more long-term results itwould be difficult to justify the use of ash with LoI values abovethe 12% limit.

The ash from the Pha Lai ash lagoons is being processed in twofacilities using a flotation method followed by drying. A new facil-ity is coming onstream to significantly increase the quantity of ashprocessing to meet the 6% limit. However, this may still not be suf-ficient for the current construction schedule. Therefore, a methodof producing more than sufficient quantities of ash with a LoI lessthan 12% has been proposed. The proposed method would helpspeed the construction process at Son La dam, and could poten-tially do so for other RCC projects.

An extensive trial mix programme was also necessary at Yeywadam. Fly ash is not available in the country so unless a suitable eco-nomically efficient import ash was available, a natural pozzolan hadto located, investigated and tested for its suitability for applicationin the RCC dam. One of the original possibilities in terms of importoptions was to bring fly ash from Mae Moh thermal power sta-tion in Thailand. However, there were uncertainties about thesupply and transport routes which would be involved.

Instead, geological investigations to confirm the pozzolanic prop-erties of materials from the different sources were undertaken toselect the most suitable site for the development of milling facili-ties. Two natural pozzolans were located near Mount Popa andhave exhibited exceptional performances when used with locallyavailable Portland cements. After extensive tests, both in the lab-oratory and in the field, the optimum mixture proportions of theRCC was found to be 75kg/m3 of Portland cement and 145kg/m3

of natural pozzolan, which is an economic set of mixture propor-tions. The success of this clearly demonstrates the advantage ofstarting a trial RCC mix programme as early as possible during thedesign phase of the project.

The accelerated rate of construction that is needed for RCCdams is well illustrated in the case of Yeywa. RCC placement beganin February 2006. Within 14 months, which also of course includ-ed the rainy season, approximately 1M m3 of RCC was placed,with the monthly production rate reaching a maximum of morethan 91,000m3. Compared to the original schedule, the dam isexpected to be completed eight months early, by the end of 2008.The project’s turbines are set to be running by the end of 2009.

Such an accomplishment has been attributed to the minimalinterference and cross structures, thereby ensuring continuity ofRCC placement. In addition, the high-cementitious contentapproach to RCC and the highly efficient, 480m3/hr nominalcapacity of the batching plant also have been important con-tributing factors.

Other factors include appreciation of the fact that speed will con-tribute to the lift joint quality by maintaining hot joints. Thishelped to release the contractor from time-consuming joint prepa-rations which helped progress and enhance the overall quality ofthe dam.

Tribute has also been paid to CGGC Gezhouba, the RCC con-tractor from China. Its extensive experience of RCC dams has beendescribed as being invaluable.

Son La, in comparison, is just getting underway with its RCCplacement under a tight construction schedule. Given the high-cementitious RCC mix design (>150kg/m3) and retarding the setperiod of the concrete to up to a day for the bottom part of thedam the maximum daily volume of RCC placed would be approx-imately 5,000m3 in layer volume. The overall average monthlyRCC production at the dam rate is seen at approximately84,000m3.

The dam was designed in accordance to international standards

LaosProject site

Son La

Myanmar

Thailand

Cambodia

Singapore

Malaysia

Indian Ocean

Andaman Sea

South China Sea

Bay ofBengal

China

Vietnam

YeywaProject site

Project name check: who’s who?Yeywa:

• Colenco Power Engineering Ltd. (Switzerland): Design and general supervision.

• Department of Hydropower, Ministry of Electric Power (Myanmar): Ownerinvolved in supplying RCC and executing civil works.

• CGGC Gezhouba (PR China): RCC contractor.

• Dr. Malcolm Dunstan & Associates (UK) & Francisco Ortega SantozConsulting Engineers (Germany): RCC expert.

• High Tech Concrete Technology (Myanmar): RCC production and supply.

Son La:

• Colenco Power Engineering Ltd. (Switzerland): Sub-consultant &RCC dam design.

• Dr. Malcolm Dunstan & Associates (UK): RCC expert.

• Electricity of Vietnam (Vietnam): Owner.

• Power Engineering Consultancy Company No. 1 (Vietnam): Main consultant.

• SMEC International (Australia): Construction supervision.

• Song Da No. 5 (Vietnam): RCC production and supply.

• Song Da No. 9 (Vietnam): RCC contractor.

Figure 1 – Location map


RCC

and checked against the Vietnamese /Russian standards. Thedesign criteria developed for the project were formulated specifi-cally as a Vietnamese standard by drawing upon the US ArmyCorps of Engineers’ Engineering Manuals (EM 1110-2-2200) andalso the US Federal Energy Regulatory Commission (FERC)Guidelines, from 2002.

A two-stage structural analysis was performed involving rigidbody and finite element (FE) modelling, and thermal modelling.The rigid body analysis examined sliding and overturning stabil-ity, the FE analysis calculating internal stresses within the damstructure. In addition, static and dynamic analyses were carriedout, looking at tensile stresses under earthquake loading, to helpin establishing the quality of RCC required and the mix design.

For the analyses, the assumed density of RCC was 2.5 tonnes/m3

and a compressive strength taken as 16MPa. From the models, thejoint tensile strengths calculated were 0.8MPa for static loadingand 1.2MPa under seismic loading.

Differential strain due to stresses were also calculated using thestatic FE analyses. The models helped determine the estimated dif-ferential deformation between the dam and powerhouse at thedownstream toe, and between the dam and the penstocks downthe downstream face. The maximum differential deformation ofthe penstock due to water load with the reservoir: at operating levelwere 4mm (vertical) and 21mm (horizontal); at maximum floodlevel were 4mm (vertical) and 23mm (horizontal).

In addition, the designers were also able to determine throughthe dynamic analyses athat the number of times the allowable stresswould be exceeded during the maximum credible earthquake(MCE) was very small, and that it was expected that only microcracking would be anticipated due to such a load.

In terms of the thermal analysis, data used were derived fromlaboratory tests, including specific heat, conductivity, diffusivitythermal expansion and adiabatic temperature rise. The model con-sidered the proposed placement sequence within the monoliths

including start and completion dates of the blocks and a linear rateof increase of the upper surface, modelled with 2m high steps. Thefoundation was modelled to 10m below foundation level. With aplacing temperature of 22°C, the maximum temperature in thedam was calculated to be 40.7°C - less than generally acceptedvalue of 45°C. IWP& DC

Right bank

Section B-BSection A-A

Left bank200

100

0

SpillwayKink197.0 A B

A B

800 500 100

0 50 100 m

LC

LCLC

64.469.36

197.0197.0

3 LC

11

13

64A

3A.1 3B.13A.2 3B.2

4B0

LIC

89

9

12

1210

10

4B

3B.13A.13A.2

4A3B.2

7

7

5

5+ 1 2

13

11

6

1 2

8

197.00

65.00

110.00117.00

0 20 m

97.00

60.00

RCC

RCC

G.E.V.RC.V.C

FSL.185.00

MOL.150.00

Right bank

Right bank section

Left bankKink at front

Dam crest

Spillway Penstocks

Diversion tunnels

Powerhouse

197.00

97.7062.00

0 50 m

0.81

C.V.C

Top: Figure 2 – RCC placing sequences, viewed from upstream

Bottom: Figure 3 – Left: Section through dam and spillway; Right: Damlongitudinal elevation from downstream

References1. Kyaw, U.W., Zaw, U.M., Dredge, A., Fischer, P. & Steiger, K.M. (2006)“Yeywa Hydropower Project, an Overview”. HydroAsia 2006

2. Kyi, U.W., Lat, U.K., Dunstan, M.R.H. & Min San, U.Z. (2006). “Trial mixprogrammes and full-scale trials for Yeywa HPP using a new naturalpozzolan”. HydroAsia 2006

3. Koe, U.A., Ortega, F.S., Naing, U.A.Z. & Knoll, K. (2006). “ConstructionPlanning, Concrete Production Equipment and Cooling Plants at YeywaHPP, Myanmar”. HydroAsia 2006

4. Dredge, A., Hung, D.T., Morris, D. & Thang, N.Q. (2008). “The Son LaHydropower Project RCC Dam”. 2nd Int. Symposium on Water Resourcesand Renewable Energy Development in Asia. Vietnam.

5. Dredge, A., Dunstan, M.R.H., Hung, D.T., Morris, D. & Thang, N.Q.(2008). “Design and preliminary Full-Scale Trial for Son La RCC Dam”. 2ndInt. Symposium on Water Resources and Renewable Energy Developmentin Asia. Vietnam.

6. Thang, N.Q., Hung, D.T., Kyaw, U. W., Conrad, M., Steiger, K.-M. &Dunstan, M.R.H. (2007). “Advantages of Roller Compacted Concrete(RCC) Gravity Dams – Two Examples in Southeast Asia”. 4th German DamsSymposium - Conference and exhibition of Deutsches TalsperrenCommittee (DTK), Freising near Munich, Germany. September 2007.

7. Francisco Ortega S. (2007). “Construction of Yeywa hydropower projectin Myanmar – focus on RCC technology”. 4th German Dams Symposium -Conference and exhibition of Deutsches Talsperren Committee (DTK),Freising near Munich, Germany. September 2007.

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CHINA’S AP1000A FOUNDATION FOR SELF-RELIANCE

NORTH KOREA AFTER THE BOMBLOAD FACTOR LEAGUE TABLES

THE FIRST PROLIFERATOR


ENGINEERINGNUCLEAR

The Power Group

with those of the structure system when Lagrangian approach is con-sidered in the formulations. To obtain the coupled equations of thefluid-structure system, the determination of the interface conditionis required. Because the fluid is assumed to be inviscid, only the dis-placement in the normal direction to the interface is continuous atthe interface of the system. Using the interface condition, the equa-tions of motion of the coupled system to ground motion includedamping effects.

Damage Criteria for Arch DamsThe earthquake performance of arch dams is evaluated in accor-dance with displacements, stresses, demand-capacity ratios (DCR)and the cumulative inelastic duration. DCR for arch dams isdefined as the ratio of the calculated arch or cantilever stresses totensile strength of the concrete used in the dam. The dam responseto the maximum design earthquake is considered to be within thelinear elastic range of behaviour with little or no possibility ofdamage if computed DCR values are less than or equal to 1.

The dam is considered to exhibit nonlinear response in the formof opening and closing of contraction joints and cracking of thehorizontal joints (lift lines) and concrete if the estimated DCRvalues exceed 1. The level of nonlinear response or opening andcracking of concrete is considered acceptable if the DCR value<2,the overstressed region is limited to 20% of the dam surface area,and the cumulative inelastic duration falls below the performancecurve given in Fig. 1. The maximum permitted DCR for linearanalysis of concrete dams is 2.

The cumulative inelastic duration in Fig. 1 refers to the totalduration of all stress excursions beyond a certain level of DCR.

MANY studies have been done to determine thedynamic behaviour of arch dams. In the research,many theoretical and experimental studies have beenpresented: from how can be arch dams modelled to

what kind of initial and boundary conditions can be used whenanalysing; from factors affecting seismic behaviour to examinationof stochastic and deterministic linear and nonlinear analyses; fromreservoir sediment effects to dam-reservoir-foundation interaction.

Reservoirs do have a considerable affect on the dynamicresponse of dams during earthquakes, and three approaches areused to consider such: the Westergaard, Euler and Lagrangianapproaches.

In the Westergaard approach it is considered that a vibratedmass dispersion with the dam is similar to hydrodynamic dis-persion towards the upstream face of the dam. In the Eulerianapproach, the displacements are the variables in the structureand pressures the variables in the fluid. In the Lagrangianapproach, however, the displacements are the variables in boththe fluid and the structure. There is no need, therefore, for anyextra interface equations in the Lagrangian approaches, and socompatibility and equilibrium are automatically satisfied at thenodes along the interfaces between fluid and structure.

Nonlinear procedures are required to asses the seismic damagelevel of concrete arch dams in earthquake-prone areas. However, itis generally known that nonlinear time history analysis of 3D archdam-reservoir-foundation system demands too much memory andtime on computers. It is also possible to use linear procedures forqualitative estimating of the damage level of concrete dams subjectedto earthquakes[15-16].

This paper illustrates the application of linear time-historyanalysis for the earthquake response computations of an archdam with the objective calculating the dynamic characteristics ofthe dam-reservoir-foundation system - i.e. dam displacement andstress response histories under horizontal component of earth-quake motions. In addition, the paper examines the use ofdemand-capacity ratios to assess the seismic performance of thedam by Lagrangian approach.

Finite Element Formulation of Fluid and Fluid-Structure SystemsIn the Lagrangian approach, fluid is assumed to be linearly elastic,inviscid and irrotational[17-18]. Rotational stress relationships arecalculated the bulk modulus and the volumetric strains of the fluid,respectively. Rotations and constraint parameters are included in thestress-strain relationship.

In this study, the equations of motion of the fluid system wereobtained using energy principles. Finite element (FE) approximationwas employed to evaluate the total strain energy of the fluid systemusing a nodal displacement vector and the stiffness matrix of thesystem, respectively.

An important behaviour of fluid systems is the ability to displacewithout a change in volume, and for reservoir this movement isknown as sloshing waves in which the displacement is vertical withan increase in the potential energy of the system due to the free sur-face motion.

The equations of motion of the fluid system have a similar form


SEISMIC ANALYSIS

Seismic damage assessment of arch dams, including dam-reservoir-foundations interactionoking seriously is examined using demand-capacity ratios obtained from linear analysis,and earthquake case studies show where further, nonlinear, studies would be required

Seismic damage assesment at acoupled dam system using DCRs

Figure 1 – Performance curve for linear elastic analysis of arch dams[16]


SEISMIC ANALYSIS

SEISMIC DAMAGE ASSESSMENT OF ARCH DAMSA double curvature Type-5 arch dam, which was suggested in‘‘Arch Dams’’ symposium in England in 1968, is selected as anumerical example[23]. The geometric properties of Type-5 archdam are given in Fig. 2.

The height of dam selected is 120m and its computed thickness damat the top and base are 5.35m and 23.35m, respectively. Type-5 archdam is developed considering reservoir and foundation. Finite elementmodel of downstream face of Type-5 arch dam, and sections and nodeselected for comparison of the results are given in Fig. 3.

There are three unknown displacements at each nodal point in dam,foundation and reservoir FE model, and there are 4355 nodes and3188 finite elements used in modelling the coupled system - the dam,foundation and reservoir having 148 solid, 1560 solid and 1480 fluidfinite elements, respectively. The ratio of Young’s modulus for thefoundatio to the concrete is 0.643, and the foundation model isassumed to be massless rock and extends downstream for the equiv-alent of the heinght of the dam (H), 3H in the upstream direction andH to the right and left.

Reservoir model is developed by using fluid element and is extend-ed as 3H. At the reservoir-dam and reservoir-foundation interface,length of coupling element is chosen as 0.001m. The main objectiveof the couplings are to hold equal the displacements between two rec-

iprocal nodes. Element matrices are computed using the Gauss numer-ical integration technique[20]. The Newmark method is used in thesolution of the equation of motions, and Rayleigh damping is con-sidered in the analyses and damping ratio is selected as 5%. Linearanalyses of coupled system are carried out by using ANSYS finite ele-ment program[24]. The material properties and element types used inthe analysis are summarised in Table1.

Linear analyses are performed using three different groundmotions - the earthquakes at Parkfield (1966), Imperial Valley(1940), and Mammoth Lakes (1980) - which were recorded. Theywere selected as they had approximately the same peak ground accel-eration (PGA). The properties of the ground motions are given inTable 2. For reasons of computational memory needs, only the first12 seconds of the ground motion time histories - but this is the mosteffective duration - is used in the analysis.

DisplacementsThe variation of maximum horizontal displacements on the cen-tral cross-section (II-II in Fig.3) of the Type-5 arch dam, obtainedfrom linear analyses for Parkfield, Imperial Valley, and MammothLakes ground motions, are depicted in Fig. 4. The maximum dis-placements, obtained along the crest point and its values are 5.3cm,6.6cm, and 7.8cm for Parkfield, Imperial Valley, and MammothLakes earthquakes, respectively.

The variation of maximum horizontal displacements along thecrest of arch dam for each ground motion are plotted in Fig. 5.

The time histories of horizontal displacements in upstream-downstream direction at the top, central FE nodal point on thedownstream face of the crest (nodal point 48 in Fig.3) of the archdam are plotted for each ground motion, in Fig. 6 (a-c). The timehistories of the displacements shows similar variation with earth-quake ground motions.

The contours of maximum displacements of dam-reservoir-foun-dation system for all earthquake ground motions are also be calac-ulated. The displacement contours represent the distribution of the

Level C0 C1 C2 C3 C4 C5 C6

Radius (unit) 3.67 5.29 6.64 7.72 8.54 8.80 8.50

Central Angle 80o 86o 92o 98o 104o 106o 106o

Figure 2 – The view in plan and vertical crown cross section of Type-5 arch dam.

Figure 3 – Finite element model of downstream face of the dam.

Table 1. Material properties ofdam-reservoir-foundation system.

Material Properties

ANSYS Elasticity Poisson Mass Compressive TensileElement Modulus Ratio Density Strength Strength

Type (MPa) (kg/m3) (MPa) (MPa)

Dam Solid 45 3.31E4 0,152 2476 30 3

Reservoir Fluid 80 2.07E3 - 1000 - -

Foundation Solid 45 2.1E4 0,3 0 - -

Table 2. Properties ofground motion records usedin the analyses.No Earthquake Date Station Component Peak Acce. Magnitude

1 Parkfield 1966/06/28 1438 PARKF/ 0.357g M (6.1)Temblor TMB205pre-1969

2 Imperial 1940/05/19 117 El IMPVALL/ 0.313g M (7.0)Valley Centro I-ELC180

Array

3 Mammoth 1980/05/27 54214 MAMMOTH/ 0.408g M (6.0)Lakes Long L-LUL090

Valley dam


SEISMIC ANALYSIS

peak values reached by the maximum displacement at each pointwithin the section. Peak values of the displacements occur near thecrest centre of the arch dam for all selected ground motions.

Principal StressesThe variation of maximum and minimum principal stresses alonglength and height of the dam (I-I and II-II sections in Fig. 3) areplotted in Fig. 7 and Fig. 8 for each ground motion. The biggestvalues of the maximum and minimum principal stresses forParkfield, Imperial Valley and Mammoth Lakes earthquakes areshown in Table 3. It can be seen from Fig. 7 that the maximum andminimum principal stresses obtained from Mammoth Lakes earth-quake records along dam length at section I-I are generally biggerthan those of Parkfield and Imperial Valley earthquake records.However, maximum principal stresses obtained from Parkfieldearthquake record near the crest at section II-II are bigger thanthose of the other two earthquakes.

The contours of maximum principal stress of dam-reservoir-foun-dation system for all earthquake ground motions are also calculated.These principal stress contours represent the distribution of the peakvalues reached by the maximum principal stress at each point withinthe section. Maximum principal stresses, which are maximum tensilestress, generally occur near the crest level.

Demand-Capacity RatiosThe time histories of maximum principal stresses (tensile stress)at nodal point 48, which is the most representative crest point ofdownstream side of the dam, for each ground motion are plottedby displaying the demand-capacity ratios (DCR) in Fig. 9 (a-c). Ifthe size effect is considered, the tensile strength of mass concretein relatively thick arch-gravity dams drops to below 3 to4MPa[26]. In this study, tensile strength of concrete material isselected as 3 MPa. It is clear from Fig. 9 that some values of max-imum principal stresses are over than DCR=1 for all groundmotions. It means that the maximum principal stresses thatoccurred on the dam are much more than tensile strength of con-crete used in dam body.

The performance curves at nodal point 48 of the arch dam arepresented in Fig. 10 for each ground motion. The level of nonlinearresponse or opening construction joints and/or cracking of concreteis considered acceptable if the DCR value<2[16].

The results shows that DCRs for Imperial Valley andMammoth Lakes earthquake records are less than 2 and thecumulative inelastic durations at all DCRs almost falls below theacceptance curve. It can be stated that the linear analyses of dam-reservoir-foundation system is sufficient for Imperial Valley andMammoth Lakes earthquake records and no or little damage mayoccur on the dam body.

However, the DCRs from Parkfield earthquake record exceed2 and the cumulative inelastic duration is substantially greaterthan the acceptable level. It is thought that Parkfield earthquakerecord would cause significant damage on the dam body.Therefore, nonlinear analysis of the coupled system underParkfield earthquake record would be required for more accurateestimate of the damage.

It can be generally stated, therefore, that earthquake groundmotions which have approximately same PGA can be demon-strated to experience different damage levels. Therefore, DCRsshould be determined for different earthquake records beforemaking a decision on the controlling and designing of existing andnew arch dams.

Figure 4 – The variation of maximum horizontal displacements on II-IIsection of arch dam.

IWP& DC

Figure 5 – The variation of maximum horizontal displacements along thecrest of arch dam.

(a) Parkfield (b) Imperial Valley (c) Mammoth Lakes(1966) (1940) (1980)

Figure 6 – The time histories of horizontal displacements at the nodalpoint 48 of arch dam.

Figure 7 – The maximum (a) and minimum (b) principal stresses atsection I-I of arch dam.

(a) (b)

Figure 8 – The maximum (a) and minimum (b) principal stresses atsection II-II of arch dam.

(a) (b)


SEISMIC ANALYSIS

References1. Oliveira, S. & Faria, R. (2006). “Numerical Simulation of CollapseScenarios in Reduced Scale Tests of Arch Dams”. Engineering Structures28 (2006) 1430–1439.

2. Alves, S. W. & Hall, J. F. (2006). “System Identification of a ConcreteArch Dam and Calibration of Its Finite Element Model”. EarthquakeEngineering and Structural Dynamics, 35 (2006), 1321-1337.

3. Shahkarami, A., Delforouzi, M. & Salarirad, H. (2004). “Study of theCompression and Tension Factors of Safety with a 3D FE Model for an ArchDam and Rock Foundation: A Case Study Of The KarunIII Arch Dam in Iran”.International Journal of Rock Mechanics and Mining Sciences (IJRM&MS),Vol. 41, No. 3, 2004.

4. She, C. X. (2004). “Deformation and Stability of the Right Arch DamAbutment of the Danjiang Hydro-power Project, China”. (IJRM&MS), Vol 41(2004) 517.

5. Lotfi, V. & Espandar, R. (2004). “Seismic Analysis of Concrete ArchDams by Combined Discrete Crack and Non-orthogonal Smeared CrackTechnique”. Engineering Structures 26 (2004), 27–37.

6. Espandar, R. & Lotfi, V. (2003). “Comparison of Non-orthogonal SmearedCrack and Plasticity Models for Dynamic Analysis of Concrete Arch Dams”.Computers and Structures 81 (2003) 1461–1474.

7. Tzenkov, A. D. (2000). “Seismic Analysis of Concrete Arch Dams withContraction Joint and Nonlinear Material Models”. Ph.D. Thesis, Universityof Architecture, Civil Engineering and Geodesy, Bulgaria, 2001.

8. Li, S., Chen, Y., Li, J. & Yang, J. (2000). “The New Method of Arch DamStress Calculation and the Application of GTSTRUDL CAE/CAD System”.Advances in Engineering Software 31 (2000) 303–307.

9. Nasserzarea, J., Leib, Y. & Eskandari-Shiria, S. (2000). “Computation ofNatural Frequencies and Mode Shapes of Arch Dams as an InverseProblem”. Advances in Engineering Software 31 (2000) 827-836.

10. Ghanaat, Y., Hall, R. L., & Redpath, B. B. (2000). “Measurement ofDynamic Response of Arch Dams Including Interaction Effects”. TwelfthWorld Conference on Earthquake Engineering, 2000.

11. Szczesiaka, T., Weberb, B. & Bachmannb, H. (1999). “NonuniformEarthquake Input for Arch Dam–Foundation Interaction”. Soil Dynamics andEarthquake Engineering 18 (1999) 487–493.

12. Lan, S. & Yang, J. (1997). “Nonlinear Finite Element Analysis of ArchDam - I. Constitutive Relationship”. Advances in Engineering Software 28(1997) 403-408.

13. Chopra, A. K. (1988). “Earthquake Response Analysis of ConcreteDams”. In: Jansen, R. B., editor, Advanced Dam Engineering for Design,Construction, and Rehabilitation, New York: Chapter 15, 1988.

14. Lee, J. & Fenves, G. L. (1998). “A plastic-Damage Concrete Model forEarthquake Analysis of Dams”. Earthquake Engineering Structural Dynamic27 (1998), 937-956.

15. Ghanaat, Y. (2002). “Seismic Performance and Damage Criteria forConcrete Dams”. 3rd US-Japan Workshop on Advanced Research onEarthquake Engineering for Dams, San Diego, California, 2002.

16. US Army Corps of Engineers. (2003). “Time-History Dynamic Analysisof Concrete Hydraulic Structures”. Engineering and Design, 2003.

17. Wilson, E. L. & Khalvati, M. (1983). “Finite Elements for the DynamicAnalysis of Fluid-Solid Systems”. Int. Journal for Numerical Methods inEngineering, 19 (1983), 1657-1668.

18. Calayır, Y. (1994). “Dynamic Analysis of Concrete Gravity Dams usingthe Eulerian and Lagrangian Approaches”. Ph.D. Thesis, KaradenizTechnical University, Trabzon, Turkey, 1994 (in Turkish).

19. Zienkiewicz, O. C. & Taylor, R. L. (1989). “The Finite ElementMethod”. Vol. I: Mc Graw-Hill, 1989.

20. Bathe, K. J. (1996). “Finite Element Procedures in EngineeringAnalysis”. Englewood Cliffs, New Jersey: Prentice-Hall, 1996.

21. Clough, R. W. & Penzien, J. (1993). “Dynamics of Structures”.Singapore, Mcgraw-Hill Book Company, 1993.

22. Akkas, N., Akay, H. U. & Yılmaz, C. (1979). “Applicability of General-Purpose Finite Element Programs in Solid-Fluid Interaction Problems”.Computers and Structures, 10 (1979), 773-783.

23. “Arch Dams, A Review of British Research and Development”.Symposium, Inst. of Civil Engineers, London, England, 1968.

24. ANSYS, Swanson Analysis System, US, 2003.

25. PEER (Pacific Earthquake Engineering Research Centre),Http://Peer.Berkeley.Edu/Mcat/Data, 2006.

26. Wieland, M. (2005). “Review of Seismic Design Criteria of Large Concreteand Embankment Dams”. 73rd Annual Meeting of ICOLD Tehran, Iran, 2005.

Table 3. The maximumcompression and tensile principalstresses from linear analyses.Earthquake I-I Section II-II Section

MaxPS1 MinPS2 MaxPS1 MinPS2(MPa) (MPa) (MPa) (MPa)

Parkfield 3.7 -4.4 7.7 -7.8

ImperialValley 4.9 -4.1 5.5 -5.7

Mammoth Lakes 4.8 -3.8 6.3 -4.9

1 MaxPS: Maximum Principal Stress (Maximum Tensile Stress)2 MinPS: Minimum Principal Stress (Maximum Compressive Stress)

(a) Parkfield (b) Imperial Valley (c) Mammoth Lakes(1966) (1940) (1980)

Figure 9 – The time histories of maximum principal stresses at nodal point 48of the arch dam for each ground motion.

Bayraktar, A. Karadeniz Technical University, Departmentof Civil Engineering, 61080, Trabzon, TURKEY

Sev, B.M. Karadeniz Technical University, Department ofCivil Engineering, 61080, Trabzon, TURKEY

Calayir, Y. Fırat University, Department of CivilEngineering, Elazı, TURKEY

Akkose, M. Karadeniz Technical University, Department ofCivil Engineering, 61080, Trabzon, TURKEY

Contact: Alemdar BAYRAKTAR, Professor.Tel: + 90 462 377 26 53Fax: + 90 462 377 26 06

E-mail: [email protected]

Figure 10 – Performance curves at nodal point 48 for each ground motion.

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FLOOD MANAGEMENTCLIMATE CHANGE

Although flood defence is a familiarproblem in the UK climate change will make the issue far more important.New and expanded solutions w ill beneeded, as Karl Hall reports

Although flood defence is a familiarproblem in the UK, climate change will make the issue far more important.New and expanded solutions w ill beneeded, as Karl Hall reports

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The pathways for flooding are generally by river (fluvial) flood-ing, coastal, high groundwater levels and snowmelt. Sometimes therecan be a combination of factors, for instance in coastal areas wherea high tide combined with high fluvial flows and storm surge createsan unusually high water level, causing problems at both the tidaland inter-tidal zones.

What makes matters worse for the UK (although as we have seenfrom the summer floods in Europe, the problem is a global one) isthe large amount of urban development carried out in flood plainareas. Current estimates place up to five million people at risk fromriver and coastal flooding, with 10,000km2 of land at risk from riverflooding. Rising sea levels will only worsen the scenario, as many ofthe world’s major cities lie in coastal areas. London is an interest-ing example, and although it is considered quite well defended atthe moment, the future situation may be rather different.

Models have been formulated and estimates for future increaseddimensions of the Thames assume there is a risk of inundation ofparts of Hammersmith and the Victoria Embankment, GreenwichPeninsula and large areas of the lower Thames valley, in all some125 km2. Other cities at risk from rising sea levels include Cardiff,Swansea, Bristol, Grimsby and Hull. At the moment there are nomodels that will definitively predict future effects from rising sealevels, but it has been estimated that average global sea levels couldrise by between 10cm and 20cm by the year 2100.

For the UK, the Intergovernmental Panel for Climate Change haspredicted a 30cm rise over the next 50 years. As a result, defenceheights will have to be raised to the tune of up to 6mm per year. Theeffects will not be constant and some areas of the UK will see moredramatic effects than others. In Scotland, for instance, sea levels haverisen at Aberdeen by 70mm since 1900 and many parts of theScottish coast are now at risk from coastal flooding, particularlybelow the 5m contour. In Scotland alone 93,000 properties are atrisk from coastal flooding, and 77,000 from inland flooding.

Some countries are now considering an alternative approach toflood management. Initiatives such as the Rhine Action Plan adopt,in principle, alternative strategies that include widening existingflood plains in conjunction with conveyance methodologies.

Factors affecting the UK include:

• Climate change and increasingly unpredictable rainfall patterns.

• Extensive coastline to all sides.

• Increased run-off from land due to agricultural practices andincreasing urbanisation.

• Long tidal rivers (Humber/Trent, Severn etc).

• Downward land tilt to some areas.

• Inadequate or poorly maintained existing drainage.

• Under-investment in flood protection schemes.

• Large catchment areas into some rivers.

• Difficulty in analysing the probability of severe weather events.

Accepting that there is little that can be done to reduce the futurerisk of flooding (although the Rio Earth Summit and Kyoto Protocolwere intended to mitigate the worsening climate situation by reduc-tions in greenhouse gas emissions), then a sustainable flood man-agement strategy can at least reduce its effects. Such a strategy mayinclude a combination of factors: reducing building on flood plains;installing additional flood defence measures; reforesting uplandareas; and allowing wider flood plains.

Implementing effective, integrated flood defence schemes requiresa considered approach, taking into account the long term effective-ness of planned measures with regard to capital cost, disruption toamenities and townscapes, downstream effects and maintenance. A

factor that is bound to compromise future flood management is theinexorable rise in demand for housing. Much of this demand is cen-tred on land that lies in flood plains near to existing major centresof population and industry. Unfortunately, some of the ‘brown’(industrial) land that the Government is insisting be re-used is alsowithin flood plains, immediately creating a conflict in those areas.It is however still early days and new planning guidance (designat-ed PPG25 and currently being developed) may help balance theneeds of developers and land users.

An effective flood protection scheme must consider factors includ-ing: the morphology of local rivers; the likely effectiveness of engi-neered flood defences; the downstream effects from theimplementation of engineered defences; and the socio-economic ben-efits that would be derived from such defences.

At present, significant amounts of public money are spent eachyear in simply maintaining existing defences, but many of thesedefences are either nearing the end of their effective lives or will beinadequate to cater for more severe floods in future. The UK’sNational Audit Office estimates that up to 40% of existing hard-engineered defences are in fair, poor or very poor condition (thoseclassified as ‘very poor’ may be considered as derelict or failed, theserepresenting 165 km of defences).

Although the government has already pledged additional capitalresources for flood defence, under the Comprehensive SpendingReview, additional investment is needed to stop long-term declineof the defences.

For coastal areas, a separate strategy may be appropriate, andshoreline management plans assess the balance of factors in termsof producing ‘sustainable policies for the coastal defence of ourshorelines taking into account natural coastal processes and issuesrelating to the environment and human needs’. Coastal effects canbe difficult to model, because alluvial morphodynamics have no real‘equilibrium’ state – what is put into effect today may be less effec-tive in future years as natural processes take effect. There is no betterillustration of this than the east coast, where loss of land is a con-tinuous process and flooding a regular event.

Intervention can have unpredictable results. Providing hard-engi-neered defences to one part of the coast can lead to the denuding ofsediment at adjacent coastal areas, requiring additional defences.Current government thinking tends towards a less-interventionistapproach, allowing natural processes to take their course (‘managedrealignment’), although this is not likely to impress the populationin these vulnerable areas unless the government introduces appro-priate compensation.

There is understandably a good deal of consternation in the publicdomain that can only be allayed by appropriate action from gov-ernment, but it is encouraging to observe that the issues are now seenas requiring a committed long-term strategy. Whatever the effects ofweather and climate turn out to be in the next hundred years, theformulating and instigation of effective flood defence schemes willrequire major political will, planning and investment, based on anholistic approach.

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IWP& DC

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physical degradation of arable land, with increased run off fromdried-out encrusted areas or saturated land. There may also be inde-terminable natural factors at work which are influencing climatechange and climatic ‘surprises’ such as changes in ocean currents,which could promote further unpredictability.

Assumptions about future climate patterns are, however, a complexmatter, and the UK has undertaken much research in this area. Theresult is a range of predictive climatological models developed by theMeteorological Office’s Hadley Centre under the auspices of theUKCIP. These assume a range of effects, based on various levels ofgreenhouse gas emissions, but whichever yardsticks are taken (low,medium low, medium-high or high, where medium-high, for instance,assumes a 1% per annum increase in CO2 emissions), the outlook isnot favourable, and wetter winters and drier summers are predicted.There is additionally the problem of predictive confidence, and whilstglobal mean temperatures and CO2 levels are considered relatively pre-dictable, factors such as climatic and regional variability are less so.

The difference between low and high predictions is very wide – itcould be as much as 20% – so there is an imperative for more accu-rate research and modelling. The problem in accurate forecastingstems from the fact that a majority of existing data is based on his-toric records and it is widely accepted that this is well out of date.Interpolations derived from existing data are therefore inappropri-ate, as this would assume that the probability of a given rainfall eventcan be calculated and preventive actions can be taken. From thismethodology, we would find that the only resolution is to designschemes to a probability of the worst case occurring approachingzero, which would result in substantially over-engineered designs.


NEW FORM

FLOODING is not a new problem for the UK, and being a nat-ural occurrence it will always be with us. But it is currentlythe frequency and severity of significant flood events that arefocusing attention on the issue, together with the real concern

that future climate patterns will worsen the outlook. Inland flooding is generally the result of high rates of run-off from

land, occasioned by intense local rainfall or by longer-term heavyrain. Most people in the UK remember the 2000 floods as beingnotably bad: it was the wettest autumn since records began andresulted in wide-scale inundation as defences were overtopped orbreached, and drainage systems overwhelmed. Around 10,000 prop-erties were flooded. These floods were in some areas 1 in 200 yearevents (flood levels that would normally be considered as having a0.5% chance of occurring), but the frequency of 100 or 200 yearevents is now increasing. Unfortunately, the historic nature of urbandevelopment has biased it towards rivers so many cities are now atconsiderable risk of regular and damaging flooding.

Hard-engineered (and therefore expensive) solutions appear to bethe only options for alleviation, at least in the short term. This phi-losophy follows on from most previous thinking, which endeav-oured to channel high-velocity flood water and discharge it to thesea in the shortest time. Although the thinking is understandable,this method of flood management has actually made some areasmore vulnerable to severe flooding at little warning.

Research suggests that by the 2080s, winter rainfall may increaseby up to 30%, with potential for greater incidence of flooding. Atthe same time, summer rainfall could decrease by up to 50%, par-ticularly in the south. As the world climate becomes warmer, greaterlevels of evaporation in summer months may be translated intoincreased rainfall and perhaps also at times later in the year thanwas previously expected. There are additional factors involved, in asometimes complex combination of events that include large-scale

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method and the dynamic analysis of concrete and embankmentdams. The methods of seismic analysis included in this report, whichoriginated in the 1970s, are still used today.

In 1989, ICOLD Bulletin 72, entitled “Selecting SeismicParameters for Large Dams”[2] was published. In this document, atwo-level seismic design concept for dams was proposed as the stateof the practice in dam engineering, ie., the operating basis earth-quake (OBE) and the maximum credible earthquake (MCE). Today,“safety evaluation earthquake” (SEE) is the term preferred to MCE.Bulletin 72 states that a dam has to be able to withstand the worstpossible ground motion to be expected at the site without cata-strophic release of the reservoir. Significant structural damage is,however, accepted as long as the dam can safely retain the reservoir.In today’s terminology, the OBE can be considered as a serviceabil-

IN the past, the pseudo-static design concept, proposed byWestergaard in the 1930s in connection with the Hoover damproject, was widely used. Several finite element programs weredeveloped in the 1970s for the dynamic earthquake analysis of

dams, based on the assumption that mass concrete and foundationrock of concrete dams behave, essentially, in the linear-elastic range.Although the first dynamic analyses of embankment dams were alsocarried out assuming linear-elastic behaviour, it was recognised thatsoil behaves inelastically under seismic excitations. Therefore, theequivalent linear method of analysis was proposed in the early1970s. In this method, the shear strain dependent dynamic shearmoduli and damping properties of soils are accounted for in a pro-cedure based on an iterative linear-elastic analysis.

In 1986, a report on the dynamic procedures for the earthquakeanalysis of dams was prepared on behalf of the Committee onAnalysis and Design of Dams of International Committee on LargeDams (ICOLD) by O. C. Zienkiewicz, R. W. Clough, and H. B.Seed[1], the leading experts in the development of the finite element


SEISMIC ANALYSIS

Analysis aspects of dams subjectedto strong ground shakingGuidance on the latest methods of nonlinear seismic analyses of dams is provided by DrMartin Wieland, Chairman, ICOLD Committee on Seismic Aspects of Dam Design

Above: Cracks along lift joints at part of upstream face of Sefid Rud buttressdam caused by the 1990 Manjil earthquake, Iran. Inelastic dynamic analysisis required to evaluate the seismic behaviour of the cracked dam


ity limit state whereas the SEE is akin to the ultimate limit state forthe earthquake loading.

For the OBE, the linear-elastic analysis methods that were devel-oped in the 1970s are still suitable. The great advantage of linear-elastic dynamic analyses is that two engineers performing the sameanalysis with two different computer programs will get identicalanswers if the geometry, material properties and boundary condi-tions are the same.

In the case of the SEE ground motions, some structural damageis accepted, which is usually characterised by inelastic phenomena,eg., joint opening, formation of cracks, plastification, hystereticbehaviour of materials, sliding and rocking motions, build up of porepressure, etc. It is obvious that inelastic or nonlinear seismic analy-sis have to be carried out in view of the performance criteria fordams under the SEE ground motions. The inelastic dynamic analy-ses are much more demanding and complex than any linear-elasticanalysis, and a lot of experience, engineering judgment and a thor-ough understanding of the main inelastic features governing thedynamic response are needed. In addition, these analyses require anin depth knowledge of the numerical limitations of the nonlinearalgorithms involved.

Many engineers still try to avoid nonlinear seismic analyses, forexample, by assuming high damping values or considering too lowSEE ground motions to reduce the dynamic response substantially,so that a linear-elastic analysis could be justified. It is, however,expected that there will be an increasing demand for nonlineardynamic analyses of dams in the future.

In the following sections, the different phenomena that may requireinelastic earthquake analyses are discussed. The emphasis in this paperis on the dynamic response of a dam to ground shaking. Other seis-mic safety aspects, such as fault movements in dam foundations ormass movements into the reservoir causing impulsive waves, are out-side the scope of this paper.

INELASTIC DEFORMATION OF CONCRETE DAMS:JOINTS AND CRACKS

Observations of earthquake damage in concrete gravity dams showthat ground shaking results in the formation of cracks in the highlystressed, central crest region along some weak planes, such as hori-zontal lift surfaces and grouted vertical contraction joints.

As no arch dam has so far suffered serious damage during earth-quake ground shaking, little experience exists about the possibledamage caused in an arch dam by, for example, the SEE. However,linear-elastic dynamic analyses show that tensile stresses exceedingthe dynamic tensile strength of mass concrete could occur in an archdam during a strong earthquake. Therefore, cracks can also beexpected to develop in an arch dam during a strong earthquakealong the contraction and lift joints, which exhibit a smaller tensilestrength than the surrounding mass concrete.

The typical blockwise construction of a concrete dam with hori-zontal lift joints at 2m-3m spacing facilitates the formation of hor-izontal cracks during a strong earthquake. Most of the deformationsof a dam would be confined to these cracks, due to which furthercracking is prevented in the dam body. Thus, it can be expected thatonly a few cracks will be formed in a concrete dam during severeground shaking.

In order to predict the behaviour of a concrete dam during the SEE,and to check the stability of a cracked dam, nonlinear seismic analy-ses would be required and the following approaches are used:

(i) smeared crack approach, in which concrete cracking is imple-mented in the constitutive model of mass concrete (continuumapproach);

(ii) the discrete modelling of contraction, base and lift joints in thefinite element model of the dam, assuming concrete and rock to belinear-elastic materials; and,

(iii) the discrete crack approach, in which the dynamic behav-iour of rigid concrete blocks separated by cracks and/or joints isinvestigated (rigid body approach).

In approach (i), the smeared crack method requires a concretemodel with quite a large number of material parameters, which aredifficult to obtain. At present, approaches (ii) and (iii) appear to bebetter suited for practical applications. For the latter method, knowl-edge of only the friction coefficient at the base of the detached rigidblock is needed. The probable sizes of characteristic concrete blocks,which could form during an earthquake, have to be determinedbased on practical experience with similar dams, engineering judg-ment, experimental investigations, and the results of linear-elasticdynamic analyses.

A concrete block separated from the rest of the dam by the for-mation of cracks behaves essentially as a rigid body, which canexperience substantial inelastic (nonlinear) displacements in theform of rocking and sliding without actually leading to a dam fail-ure, owing to the low slenderness ratio of these dams. In fact, thedisplacements of such detached blocks could even be estimated bymeans of a simple Newmark-type sliding block analysis. If thecracks were inclined, the sliding movements may, however, be sig-nificantly larger than in the case of horizontal cracks [3][4]. Post-earthquake stability analyses should consider the uplift pressureacting on the sliding surface. The dynamic overturning stability isless of a problem as the rocking motion of a detached concreteblock is generally a reversible process.

The formation of horizontal cracks during an earthquake in thehighly stressed upper portion of a concrete dam is beneficial for thedynamic stability of detached concrete blocks. Joint openings andsliding movements at the cracks are mechanisms that ensure that amassive concrete dam can safely resist ground motions exceedingthe original design earthquake. This behaviour is comparable to thatof a ductile structure in which large inelastic deformations can takeplace without causing a disastrous collapse.

SEISMIC ASPECTS OF RCC DAMS

Most roller compacted concrete (RCC) dams are basically gravitydams and, therefore, their earthquake behaviour is also similar tothat of conventional gravity dams. As in conventional concretedams, cracks can be expected to form along horizontal lift joints.Vertical contraction joints could also open, but this is not a criticalsafety issue since gravity dams are designed to carry the loads bycantilever action and not by arch action.

The post-cracking dynamic behaviour of blocks separated bycracks and joints in an RCC dam can also be analysed using rela-tively simple rigid body models, as in the case of a conventional con-crete dam. Because of the large thickness of an RCC dam, a slidingmovement of several metres would have to occur before a detachedconcrete block would fall.

INELASTIC DEFORMATIONS OF EMBANKMENT DAMS

Basically, the seismic safety and performance of embankment damsis assessed by investigating the following aspects:• permanent (inelastic) deformations experienced during and after

an earthquake (e.g., loss of freeboard);• stability of slopes during and after the earthquake, and dynamic

slope movements;• build-up of excess pore water pressures in embankment and foun-

dation materials (soil liquefaction);• damage to filter, drainage and transition layers (i.e., whether they

will function properly after the earthquake);• damage to waterproofing elements in dam and foundation (core,

upstream concrete face or asphalt membrane, geotextiles, groutcurtain, diaphragm walls in foundation, etc.,);

• vulnerability of dam to internal erosion after formation of cracks orformation of loose material zones due to high shear (shear bands);

• vulnerability of hydromechanical equipment to ground displace-ments and vibrations; and,

• damage to intake and outlet works (safe release of the water fromthe reservoir may be jeopardised).

SEISMIC ANALYSIS


SEISMIC ANALYSIS

Most of the above aspects are directly related to seismic deforma-tions of the dam during strong ground shaking. Therefore, they aregoverned by the deformational characteristics of the fill materials.

Liquefaction is a major problem for tailings dams and small earthdams constructed of, or founded on, relatively loose cohesionlessmaterials, and used for irrigation and water supply schemes, as inmany cases they are not properly designed against earthquakes. Infact, this could be assessed based on relatively simple insitu tests. Forexample, there exist empirical relationships between SPT blowcounts and liquefaction susceptibility to different earthquake groundmotions characterised by the number of stress cycles and the peakground acceleration.

For large storage dams, the earthquake-induced permanent defor-mations must be calculated. Damage categories are, for example,expressed in terms of the ratio of crest settlement to dam height.Calculations of the permanent settlements of large rockfill or con-crete face rockfill dams (CFRDs) based on dynamic analyses are stillvery approximate as most of the dynamic soil tests are usually car-ried out on samples with a maximum aggregate size of less than 5cm.To estimate representative dynamic material properties, dynamicdirect shear or triaxial tests on large samples are needed. These testsare, however, too costly for most rockfill dams. As information onthe dynamic behaviour of rockfill published in the literature is alsoscarce, the settlement prediction involves sensitivity analyses and engi-neering judgment.

Substantial seismic settlements could occur in rockfill dams andother dams with large rock aggregates, especially if the fill materi-als have not been adequately compacted at the time of construction.In spite of large settlements, a rockfill dam could still safely with-stand a strong earthquake.

Cracks may cause failure of an embankment dam under the fol-lowing circumstances[4]:• filter, drain and transition zones are missing;• filter, drain and transition zones do not extend above the reservoir

level; or,• modern filter criteria were not used to design the dam.Transverse cracking as a result of deformations could also be animportant issue.

SEISMIC ASPECTS OF CFRDSROCKFILL DAMS

The seismic safety of a CFRD is often assumed to be superior to thatof a conventional rockfill dam with an impervious core. However,the crucial element in CFRDs is the behaviour and performance ofthe concrete slab during and after an earthquake.

The settlements of a rockfill dam caused by the MCE or SEE arerather difficult to predict and depend on the type of rockfill and thecompaction of the rockfill during dam construction. Depending onthe valley shape, dam deformations will also be non-uniform overthe upstream face, causing differential movements of the concreteface, local buckling in the compression zones, etc.

In many cases, embankment dams are analysed by the equivalentlinear method using a two-dimensional model of the highest damsection. In such a seismic analysis, only reversible elastic deforma-tions and stresses are calculated, which are relatively small and donot produce high dynamic stresses in the concrete face slab. Thesesimple models have to be complemented by models, which alsoinclude the cross-canyon component of the earthquake groundmotion as well as the inelastic deformations of the dam body. Forsuch a dynamic analysis, a three-dimensional dam model has to beused and the interface between the concrete face and the soil transi-tion zones must be modelled properly.

The concrete slab acts as a rigid diaphragm and has a deforma-tional behaviour that is very different from that of the rockfill andtransition zone materials. This may result in high in-plane stressesin the concrete slab, especially as the cross-canyon response of thedam may be restrained by the relatively rigid concrete slab. The seis-mic forces that can be transferred from the rockfill to the concreteslab are limited by the friction forces between the transition zoneand the concrete slab. Since the whole water load is supported bythe concrete slab, these friction forces are quite high and, therefore,the in-plane stresses in the concrete slab may become sufficientlylarge to cause local buckling, shearing off of the slab along the joints,or to damage the plinth.

As experience with the seismic behaviour of CFRDs is still verylimited, more efforts have to be undertaken to study the seismicbehaviour of these dams[4].

SPECIAL FEATURES OF SEISMIC ANALYSIS OFCONCRETE AND EMBANKMENT DAMS

For the dynamic analysis and seismic safety assessment of concrete andembankment dams, various features have to be considered, such as:• occurrence of earthquake (return period of different design earth-

quake ground motions);• characteristics of strong ground shaking (peak ground accelera-

tion, frequency content, duration of strong ground shaking);• spatial variation of ground motion at dam site;• superposition of static and dynamic load cases;• dynamic soil-structure interaction effects;• dam-reservoir interaction effects (shape of reservoir, compress-

ibility of water, wave absorption in reservoir bottom, wave heighteffects in reservoir, etc.,);

• dynamic material properties of concrete, soil, rockfill and foun-dation rock;

• dynamic (tensile) strength properties of concrete, soil, rockfill andfoundation rock;

• joints in concrete and rock;• effect of uplift or pore pressure in joints;• pore pressure build-up in soils;• structural damping;• corner stress concentrations;• type of numerical analysis (time domain analysis, response spec-

trum analysis, linear analysis, nonlinear analysis, etc.,);• compilation of results of time history analyses (use of maximum

response quantities for design and/or safety assessment); and,• performance criteria (allowable stresses, stability safety factors,

etc.,) for assessing the results of dynamic (and static) analyses.Many of these features call for nonlinear analyses. Due to lack of

Below: Cracking and inelastic deformations of crest of embankment damcaused by the 2001 Bhuj earthquake in India. The prediction of cracks anddamage requires nonlinear dynamic analyses and modelling of dam materials.


SEISMIC ANALYSIS

information, these features may involve considerable uncertainties,which have to be accounted for by performing sensitivity analyses.To avoid a large number of analyses, engineering judgment and con-servative assumptions are needed and often used in practice.

The seismic behaviour of dams under strong ground shaking ishard to predict, as each large dam is a prototype located at a uniquesite. Generalisation of results is often not possible or questionable.

NONLINEAR ANALYSIS ASPECTS

There are a number of general-purpose computer programs(ABAQUS, ADINA, ANSYS, FLAC, etc.) that can be used for non-linear seismic analyses of concrete and embankment dams. However,there is a lack of information on the material properties to be usedin the available nonlinear constitutive models. Therefore, it is veryimportant that the engineer first clearly formulates the problem tobe analysed taking into account the available information. A sim-plified nonlinear analysis may often be superior to a sophisticatedanalysis for which some basic information is not available.

The objectives of the nonlinear analysis are: (i) to predict the earth-quake behaviour of a dam as realistically as possible; (ii) to assessthe deformations of the dam; (iii) to assess the damage the dam willexperience; and most importantly, (iv) to assess the safety of the dam.

The following stepwise approach towards nonlinear seismicanalyses is recommended (direct time history analysis is preferredin all cases):

Concrete dams:• Linear-elastic analysis for OBE;• Newmark-type sliding block analysis of whole gravity dam struc-

ture or detached blocks in a concrete dam;• Rigid body analysis of cracked concrete (gravity, arch-gravity or

arch) dam assuming that all deformations occur along cracks orjoints, whereby cracks form along lift joints or the dam-founda-tion contact (combined rocking and sliding motion of two-dimen-sional model); and,

• Analysis of arch-gravity and arch dams with contraction jointopening, or opening of dam-foundation contact or peripheral joint(if provided).

A concrete damage model with tension failure criterion may be suit-able for monolithic dams, but it does not account for reducedstrength properties of contraction and lift joints and, therefore, may

not be better than the simple models listed above when the behav-iour of the dam under the SEE ground motions has to be analysed.

Embankment dams:• Equivalent linear dynamic analysis of dam:

Advantages: (i) substantial amount of information onshear strain dependent material properties exists, and (ii) computerprograms, such as FLUSH, QUAD4M, etc., are readily available foranalysis of two-dimensional dam sections;

Disadvantages: (i) method is almost 40 years old and doesnot properly represent the nonlinear behaviour of soil, (ii) it is cum-bersome for three-dimensional analysis, and (iii) inelastic deforma-tions are difficult to estimate based on results of dynamic analysis;• Newmark sliding block analysis (simple method for estimating

sliding movements of slopes);• Analysis using Coulomb friction elements to model interface

between transition/filter materials and impervious core, or inter-face between concrete face and supporting layer in the case of aCFRD (analysis mainly for static effects); and,

• Elastoplastic soil models (preferably using a constitutive modelwith only a few parameters).

CONCLUSIONS

A thorough understanding of the inelastic and nonlinear seismic phe-nomena, which are expected during strong ground shaking, is pre-requisite for nonlinear seismic analysis of dams.

In a concrete dam, strong ground shaking could lead to openingof contraction joints and formation of horizontal cracks along liftjoints, as a result of which high dynamic stresses are prevented inother parts of the dam. Similarly, an embankment dam may under-go significant permanent deformations during a severe earthquake.Some structural damage is accepted in a dam as long as its waterretaining function is ensured. For the seismic safety and damageassessment of concrete and embankment dams, nonlinear dynamicanalyses are often needed to determine the expected inelastic defor-mations under the SEE.

Simple nonlinear analyses methods are still widely used for theseismic analysis of dams, such as the Newmark sliding block methodand the equivalent linear method for the analysis of the embank-ment dams. These methods are, however, nearly 40 years old. Inview of an increasing demand for nonlinear methods of analysis forthe safety evaluation of existing and new dams according to the cur-rent seismic design criteria, it is recommended to update ICOLDBulletin 52 (1986), which is still based on linear-elastic concepts.

The methods for nonlinear dynamic analysis of dams are, how-ever, still under development. Nonlinear seismic analyses need sub-stantial engineering judgment. The proper formulation of the goalsof the seismic analysis is probably the most difficult task required toensure that such an analysis can actually ‘succeed’. Relatively simplemodels should be preferred to complex models employing nonlin-ear constitutive laws using parameters that are either not availableor very hard to determine.

References1. ICOLD. (1986). “Earthquake analysis procedures for dams”. (Reportprepared on behalf of the Committee on Analysis and Design of Dams ofICOLD by Zienkiewicz, O. C., Clough, R. W. & Seed, H. B.). Bulletin 52,International Commission on Large Dams (ICOLD), Paris

2. ICOLD Bulletin 72. (1989): “Selecting Seismic Parameters for LargeDams, Guidelines”. Committee on Seismic Aspects of Dam Design, ICOLD.

3. Malla S. & Wieland M. (2003). “Simple Model for Safety Assessment ofCracked Concrete Dams Subjected to Strong Ground Shaking”. 21stInternational Congress on Large Dams, ICOLD, Montreal.

4. Wieland M. (2003). “Seismic Aspects of Dams, General Report, Q.83”.Proceedings of the 21st Int Congress on Large Dams, ICOLD, Montreal.

IWP& DC

Above: a further view of damage to embankment dam due to Bhuj earthquake

would be outwith design estimates. The data could also inform bud-getary options and construction phase logistics should opportuni-ties arise, or be pursued, for improving wall roughness within theestimated range of headloss.

RESEARCH PROJECT

The 690MW Kárahnjúkar hydropower project marked the first useof TBM tunnelling in Iceland, and so there was not a large pool ofdomestic experience to draw upon to execute the works.

Design and construction of the scheme has been a significant inter-national effort, drawing upon services from local and foreign con-sultants in the client’s design engineer Kárahnjúkar Engineering JV(KEJV) – VST Consulting Engineers, Pöyry, MWH, Rafteikning andAlmenna Consulting Engineers. The design programme commencedin 2000. As local practice prevents the designer from supervisoryduties, a consortium was hired as owner’s representative - VIJV,which comprises Mott MacDonald, Linuhonnun, Hnit, Fjarhitun,Sweco, Norconsult and Coyne et Bellier.

The main contractor undertaking the KAR-14 headrace and


TUNNELLING

Looking attunnel

roughnessResearch in Kárahnjúkar headrace is

providing fresh insight into tunnel wallroughness to estimate headloss. Report

by Patrick Reynolds

Visual inspection oftunnel wall roughness

in Kárahnjúkarheadrace duringconstruction to

investigate frictionalheadlosses

Rock class range: Smooth – figures 1 and 2 Rock class range: Medium – figures 3 and 4 Rock class range: Rough – figures 5 and 6

1 2 3 4 5 6

The TBM drives for the headrace tunnel of the Kárahnjúkarhydropower scheme, in Iceland, found highly varied geo-logical conditions, particularly with the large water inflowsthat were suffered in some parts of the bores. Beyond that

tough construction experience, however, different lessons are nowbeing learned that should be useful for tunnel lining works in a widerrange of water projects thanks to client-sponsored research into sur-face, and hence hydraulic, roughness.

The client, national power company Landsvirkjun, was natural-ly focused on headloss in the hydraulic system not only for funda-mental economic reasons but also due to the potential scale of lostenergy, given that the 7.2m-7.6m diameter headrace tunnel is39.6km long. Prior to the research, design estimates used in plan-ning the project estimated the hydraulic friction losses at anywherebetween approximately 60m-95m, which is about 10%-17% of thenominal gross head of 600m under flow rate of 144m3/s, or full loadconditions.

Every percentage point saved in headloss, and even the shavingsof such, represents energy for sale to a power-hungry aluminiumsmelter operating in a hot commodity market, and also the electric-ity grid. Landsvirkjun aims to generate average energy 4600GWh/year. Beside the economic benefits to the client, though, therewould also be gains by using the greater knowledge of the insitutunnel roughness to fine-tune operational rules for the hydropowersystem.

Beyond the immediate client, other project sponsors with watertunnels in which headloss is of key importance can also draw uponthe research to help secure additional economic and operational ben-efits. To gain such, in the most effective way, they will require thesupply side services of designers and contractors to absorb theresearch findings to help estimate, monitor and adjust the surfaceroughness of tunnel lining works during the construction phase,especially so if data were to indicate that consequent energy losses

Tunnel wall roughness TBM-bored parts of Kárahnjúkar headrace was thefocus of research using visual and laser scan measurements. Above (middleand right): Shotcrete class range of roughness, from smooth to rough


Jökulsá diversion tunnel works under a re-measurement contract,and other works, is Impregilo. The headrace and diversion tunnelhave been excavated through varied volcanic and sedimentary rocksmostly by TBM with some drill and blast, though slightly more thaninitially planned. Three TBMs – two 7.2m diameter main beamshields and a 7.6m diameter machine - were supplied by Robbinsfor the project. Excavation of the headrace commenced in mid-2004and finished late 2006, and the Jökulsá bore is almost complete.

In total, the US$1.3B scheme will have approximately 73km ofhard rock tunnel, mostly unlined but with stretches of shotcretewalls, and an underground powerhouse.

The view was that the available technical data and literature onroughness of long TBM-bored water tunnels was incomplete and oflimited reliability in spite of past experience of design and operationof such bores internationally. In particular, there was a lack of goodinformation on unlined TBM-driven tunnels especially through vol-canic rock.

The idea for the tunnel roughness measurement programme camefrom the hydraulic coordinator, Gunnar Gudni Tomasson of VST,and lead headrace tunnel design engineer, Joe Kaelin of PöyryEnergy. They also supervised the studies, undertaken by others inKEJV - local firm VST in conjunction with Pöyry – and completedduring the headrace excavation. The research effort was supportedby VIJV and Impregilo.

A different, established approach - Rønn’s “IBA” method, fromNorway - was used to assessing headloss in unlined tunnels exca-vated by drill and blast. The method is one of many approaches (eg.Rahm, Colebrook, Huval, Priha, Reinius, Wright, Johansen, Solvikand Czarnota) and it is based on measurements of cross section andlongitudinal geometry over 20m-25m long portions of tunnel to cal-culate wall roughness and, hence, equivalent hydraulic friction.

To prepare for the studies on the TBM drives, the team drew uponthe methodology of wall roughness and hydraulic headloss studies,established by Pegram and Pennington in the report to the WaterResearch Commission by the University of Natal. It included thecase study of Delivery Tunnel South of the Lesotho Highlands WaterProject (LHWP), but looked at different surface types (sandstone,granite, shotcrete and concrete) in TBM-driven tunnels in general.Laser measurement was used in four tunnels, two in LHWP.

MEASUREMENTS – VISUAL INSPECTION

At Kárahnjúkar, the aim was to collect physical measurement dataduring construction along the entire length of the headrace. Visualinspections of tunnel walls were conducted at 50m intervals, exact-ly, over 2005-6.

During visual inspections, a 1m-wide strip of rock was inspectedbelow springline, at springline level and in the crown at the side ofthe tunnel, opposite the mucking out conveyor, to categorise intactrock or shotcrete into different roughness classes – smooth, mediumand rough. The classes were defined to represent the range of obser-vations and were based on measurements of the maximum averagedeviation of the wall surface from a straight bar ruler - 40cm longfor rock surfaces, 80cm long for shotcreted surfaces; they are, inprinciple, independent of geology. Additionally, the surface belowthe springline level was photographed.

Specifically, the smooth, medium and rough categorisation forrock surfaces resulted from maximum average deviations from thestraight bar ruler of <5mm, 5mm-14mm and 15mm-24mm, respec-tively. The corresponding thresholds for shotcrete lining were<10mm, 10mm-25mm and >25mm, respectively.

It should be noted, though, the processing of the data from theobservations took into account planned finishing work subsequentto inspections, eg further shotcrete applications or treatment andcleaning of surfaces. The researchers allowed for these estimatesbased on size of the sections involved and observed workmanshipand quality control on executed works.

Observed large-scale rock features, such as joints and/or pockets,were classified into four categories by the depth and number. In the

lowest category, representing rock with no such features, the classi-fications of smooth, medium and rough fell within the limits of thedeviation measurements from the bar ruler, as noted above. Themeasurement bands for smooth, medium and rough in each of thethree other, rising, categories are up 40mm, up to 100mm and inexcess of 100mm, respectively.

To aid consistency, the same hydraulic engineer was responsiblefor classifying all the surveyed surfaces. In total, almost 90% of theTBM drives were inspected visually, equating to 1893 observationsat 631 locations. The remaining 3.9 km of headrace comprised dis-continuous, inaccessible stretches during the inspection period.

In summary, a quarter of the inspected tunnel was shotcrete lined,and those sections classed as: smooth (14%); medium (64%); and,rough (22%). While rebound shotcrete prevented about 4% of theunlined rock surfaces from being classified, those assessed wereclassed as: smooth (26%); medium (65%); and, rough (9%).

In terms of the geological strata, those rocks with proportionallymore rough surfaces ranged from pillow lava, tillite, and cube joint-ed basalt in decreasing order to andesite, scoria, pillow breccia, sco-racious basalt, conglomerate, olivine basalt, porphyric basalt,tholeiitic basalt, and sandstone/conglomerate, and sandstone.

Finally, at the other end of the range, siltstone and sandstone/tuffwere classed as having no rough surfaces. However, it should benoted there were few observations of andesite, siltstone and tillite.

Observations of the range of joints and large scale irregularitiesconcluded that about 45% were sparse and/or shallow, a quarterwere dense and/or deep, a quarter were free of joints, and approxi-mately 5% of the surfaces contain large rock break-out.

In terms of geological strata, rock with many and/or deep jointswere found, in decreasing order of importance, associated with: cubejointed basalt, pillow lava, tholeitic basalt, olivine basalt, tillite,andesite, porphyric basalt, scoria, pillow breccia, scoracious basalt,sandstone/tuff, conglomerate, sandstone/conglomerate, sandstoneand siltstone.

Joint-free surfaces were found in association with: siltstone, sand-stone/conglomerate, sandstone, conglomerate, sandstone/tuff, sco-racious basalt, scoria, tillite, porphyric basalt, cube jointed basalt,olivine basalt, tholeitic basalt, pillow lava and andesite.

TUNNELLING

S

EW

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Reykjavik

Headracetunnel

Kárahnjúkar

Hálslónreservoir

Kelduárreservoir

Ufsalónreservoir

Egilsstadir

Fjaroaál

Powerhouse

Location map of the 690MW Kárahnjúkar project in Iceland and the layout ofthe almost 40km headrace tunnel and the Jökulsá diversion tunnel


TUNNELLING

MEASUREMENTS – LASER SCAN

Laser scans were executed at approximately 10% of the visuallyinspected surfaces. Rock surfaces were measured - using a FAROScan Arm portable coordinate measuring machine - below spring-line level, and shotcreted surfaces above springline level as the upperparts were lined when measurements were taken.

About 600 profiles were scanned at 73 different locations overnine months. The sites to be scanned were chosen from photographsto represent the different roughness classes, and were dry, or had tobe dried, before the scan. The scanned surfaces represented nineroughness categories - four to reflect the range within each of theclassification groups of smooth, medium and rough. In the sameapproach, the shotcrete walls were represented by three roughnesscategories.

The support platform for the scanner was bolted to the wall andthe head of the scanner fixed to a 1m long bar. Steady motion scan-ning was facilitated by a manually-operated cogwheel.

Scans were made of the walls in 40mm wide strips, each strip com-prising 640 points. The coordinates are scanned with an accuracyof 0.1mm and point spacing of less than 0.25mm. At each surveysite, the scanner measured two 40mm wide by 1m long strips, sep-arated vertically by about 100mm. Four profiles with a vertical sep-aration of 8mm were extracted from each scanned strip, whichprovided eight roughness profiles at each scan site. The averagesample spacing was 0.1mm.

DATA ANALYSIS

The data obtained from the and laser scan measurements wereprocessed according to the method developed by Pegram andPennington, which transformed the data from physical to hydraulicroughness. These drew upon three parameters: equivalent sand grainroughness, ks, also referred to as Nikuradse’s equivalent sand grainroughness; a dimensionless friction factor, f, associated with the useof the Darcy-Weisbach flow resistance formula; and, a flow resis-tance coefficient, associated with the alternative use of the technicalManning (or Strickler) flow resistance formulae. The relationshipbetween f and ks is expressed by the Colebrook-White equation.

Wall roughness in TBM-bored tunnels has a wave-like structurethat varies with geological strata as well as the operation of the cut-terhead, though data on TBM advance rates were not explicitly com-pared to intact roughness. The researchers note further that the scaleof the roughness arising from cutting speed or method is usually an

Following the visual inspection to pre-categorise the rocks into roughnessclasses, about 10% of inspection sites were scanned by wall-mounted laser


TUNNELLING

order of magnitude smaller than that due to the geology. They addthat the regular waves that were ground into strata were only visi-ble on smooth rock surfaces.

Still, the wave properties can be calculated from the laser mea-surements, which contribute to the headloss calculation by estab-lishing the dominant wave length and taking its ‘bump’, or waveheight, as an approximation to the equivalent sand grain roughness.

In the initial design estimates, the equivalent sand grain roughnessfor unlined TBM drives was taken as 10mm, and 20mm for shot-crete walls. The interpreted measurements data indicated that 40%of the unlined headrace had a larger roughness value and 60% lower.The average value for the shotcrete walls was determined to be lowerthan estimated, at 17mm.

It should be noted that the headloss effects resulting from direc-tional changes in the tunnel, such as at bends, are calculated sepa-rately as singular energy losses as commonly established in hydraulicsystem analyses. Further, in assessing the possible effects of varia-tions in tunnel cross-section, this is considered to be negligible forTBM-driven bores while those in drill and blast sections are account-ed for in established analyses, such as the IBA method.

Frictional headlosses corresponding to the full rate, design dis-charge were calculated for each roughness category using the fric-tion factors given by the Colebrook-White formula and theDarcy-Weisbach equation. Based on the calculated roughness data,and taking the 7.6m diameter TBM to have bored 14.7km and thetwo 7.2m diameter machines to have excavated a total of 20.8km,the specific headloss per unit length of the tunnel was determined.

The researchers note that the calculations showed specific headlossesfor shotcrete sections to be similar to those for rock with large break-out, partly due to the minor throttling effect of its thickness slight-ly reducing the internal diameter of the tunnel.

Based on the measurements and data analyses, the research withits elected methodology determined that the overall headloss fromfriction in the TBM-bored section of the headrace was 64m with atolerance of 10%, which puts it at the lower end of the initial designestimate. The corresponding initial estimate, based on average valuesof roughness coefficients, is 71m.

Verification work is now underway to derive the actual headlossin the headrace during operation of the power plant, which started-up last year. While the headrace is not yet carrying the full, designflow rate, only 100m3/s, so far the direct measurements show thatoperational headloss is 6% less than that predicted from the rough-ness measurements. As the discharge rate increases the headloss mea-surement will become more accurate, the researchers said.

R&D AND APPLICABILITY

The researchers say the key area for further research is toimprove the accuracy of matching the scanned data of wallroughness to the actual equivalent sand grain roughness, as thisis independent of tunnel diameter. While the operational head-loss information at Kárahnjúkar verifies understanding of therelationship it is, at the same time, a blunt instrument, to adegree, though the best yet; it is comparing the actual and esti-

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0S0 S1 S2 S3 M0 M1 M2 M3 R0 R1 R2 R3 S M R

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easu

red

loca

tions

Proportions of roughness class measurements (shotcrete at right - S,M,R) Caclucalted equivalent sand grain roughness from survey data

The laser scanned vertically-separated strips of wall surface Survey findings of proportions of roughness of rock and shotcrete surfaces

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TUNNELLING

mated values at the ‘macro’ system level and does not, for prac-tical and other reasons allow for operational investigation inindividual tunnel sections.

Their hope, therefore, is to gain backing and support to under-take a programme of laboratory tests to further refine the knowl-edge of how equivalent sand grain roughness relates to actual wallsurfaces. Such research will benefit design and construction of allwater conveyance tunnels, no matter the specific combination ofgeology, add the researchers.

In the meantime, the research as it stands also has practical appli-cation for all water tunnels, particularly so for those in which theeconomics of a project depend to a high degree on estimates of head-loss, or the energy loss is an important design factor for other rea-sons, such as calculating transients, say the researchers.

They add, though, that while the research data from the studiesonly apply directly to the geology at Kárahnjúkar and would havevalue to other drives traversing volcanic geology, the conclusionsestablished with regard to the roughness of different rock forma-tions and shotcrete surfaces are applicable to similar strata andtunnel lining elsewhere.

The research findings, therefore, can help confirm design assump-

tions through the construction phase of a project. The findings canalso assist in managing any changes to tunnel lining works thatmight possibly be required or could arguably be of longer-term ben-efit to a client.

There is always the additional possibility – especially as researchadvances - of following up the construction phase to measure actualheadloss not only to take the opportunity for a further, general checkof the headloss prediction system but also, possibly, to ensure thecontracted performance has been delivered.

IWP&DC would like to thank the research team for thebriefing, especially Kristin Martha Hakonardottir of VST,

Gunnar Gudni Tomasson of Reykjavik University andVST, and also their co-authors in a recent research paperon the work, Bela Petry of Delft Netherlands and BjornStefansson of Landsvirkjun. They also acknowledge the

initiative for and supervision of the research by Joe Kaelinof Pöyry, the visual inspections by Snorri Gislason, a

geologist at VST, and the laser scan work by René Fretz, asurvey engineer with Pöyry.

4.0

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m)

(a) 7.2 m TBM

(b) 7.6 m TBM

Top: Equivalent sand grain roughness calculated against rock typeBottom: Specific headloss ranges in different diameters of the headrace

References1. Rønn, P.-E. & Skog, M. (1997) “New method for estimation of head lossin unlined water tunnels”, Hydropower '97, Broch, Lysne, Flatabø &Helland-Hansen (eds). Balkema, Rotterdam, pp. 675-682, 1997.

2. Landsvirkjun. (2007) “Estimating the hydraulic roughness of theheadrace tunnel of the Kárahnjúkar hydroelectric plant”. Report,October 2007.

3. Pegram, G.G.S. & Pennington, M.S. (1996) “A method for estimatingthe hydraulic roughness of unlined bored tunnels”. Report to the WaterResearch Commission by the Department of Civil Engineering, University ofNatal, WRC Report No 579/1/96. ISBN No. 1 86845 219 0, 1996.

4. Viljoen, B.C. & Metcalf, J.R. (1999) “Commissioning of the LHWPDelivery Tunnel: Overview of Work Done and Results Obtained”. Tunnellingand Underground Space Technology, Vol. 14, No. 1, pp. 37-54, 1999.

5. Boeriu, P. & Doandes, V. (1997) “A new method for in situ determinationof the roughness coefficient of the hydropower plant tunnels”. Hydropower'97, Broch, Lysne, Flatabø & Helland-Hansen (eds). Balkema, Rotterdam,pp. 575-580, 1997

6. Hakonardottir, K.M., Tomasson, G.G., Petry, B. & Stefansson, B. (2007)“Evaluating the hydraulic roughness of unlined TBM-bored waterconveyance tunnels: a measurements programme in the headrace tunnel ofKárahnjúkar HEP”. Hydro 2007, Grenada, Spain. October 2007.

7. Garnayak, M.K. (2001) “Hydraulic head losses in an unlined pressuretunnel of a high head power plant: theoretical approach and comparisonwith measured results – Case study of Chimay Hydropower Project, Peru”.Postgraduate Diploma Project, Hydraulics lab (LCH), Ecole PolytechniqueFederale de Lausanne, 1999-2001.

8. Metcalf, J.R., & Jordaan, J.M. (1991) “Hydraulic roughness change inthe Orange-Fish Tunnel: 1975-1990”. The Civil Engineer in South Africa,August 1991.

9. Petrofsky, A.M. (1964) “Contractor’s view on unlined tunnels”. Journalof the Power Division, Proceedings of the American Society of CivilEngineers, October 1964.

10. Dann, H.E. (1964) “Unlined tunnels of the Snowy Mountains Hydro-electric Authority, Australia”. Journal of the Power Division, Proceedings ofthe American Society of Civil Engineers, October 1964.

11. Czarnota, Z. (1986) “Hydraulics of rock tunnels”. HydraulicsLaboratory of The Royal Institute of Technology, Stockholm, 1986.

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IWP& DC


TECHNOLOGYFLOOD MANAGEMENT

THERE are many alternatives to sandbags on the market,and undoubtedly with the recent flooding witnessed in theUK, Europe and the US, countless more are on the way.One such alternative is AquaFence – a semi-mobile flood

protection system that has been in development since 1997 and infull production since 2005.

The system has been developed over a ten-year period to ensureits suitability for use in a live flood situation. The system is areplacement for the traditional sandbag wall that is used for floodprotection the world over, and has the possibilities to improve reac-tion time and effectiveness in most situations where property isthreatened by flood water.

Although sandbags are the most common form of flood protec-tion, they are notoriously time and manpower intensive to set-up– on average a ten-man team can take up to 72 hours to erect a100m sandbag wall. In known flooding areas, this can often meanthat hundreds of workers and volunteers are required to spenddays preparing for a coming flood. Testing has, however, confirmedthat an AquaFence flood wall of 100m length can actually be set

up by ten men in one hour. One such area where hundreds ofpeople were needed to prepare for regular local flooding is MountVernon in Washington, US. When the Skagit river threatens theMount Vernon Downtown district, it takes hundreds of volunteersand city workers 12 to 15 hours to set up a sandbag wall.AquaFence needs just a small team of workers to set-up flooddefence in about a third of the time.

Mount Vernon’s state-of-the-art AquaFence flood fighting arse-nal was shown to the rest of the country after the town took deliv-ery of its AquaFence system in September. At a demonstration heldon 24 September, the entire system was installed in just four hours,with a team of 16 people. The AquaFence flood wall was erectedalong Mount Vernon’s Main Street, stretching from Division St. toKincaid St., a total of 460m in length.

This particular installation was used to train the local authorityworkers on exactly how to use AquaFence. A key aspect of thesystem is its ease of use but Mount Vernon was keen to ensure itsstaff could harness the set-up time of AquaFence the moment it isneeded in a live flood situation. The reaction to AquaFence at

A flexible semi-mobile flood protection system has been developed toaddress failings in traditional flood protection measures such as highcosts, low strength, water leakage and slow deployment

Alternative protection


TECHNOLOGYFLOOD MANAGEMENT

Mount Vernon was positive and the company’s US division, basedin Lynwood, Washington, is expecting to see more towns show aninterest in the system as a result of the demonstration.

DESIGN ELEMENTS

One AquaFence element actually replaces approximately 900 sand-bags. The short set-up time of AquaFence is achieved through this,and the all-in-one design of the AquaFence sections (elements).Each 200cm wide and 120cm high (as standard, other heightsavailable) element is self-contained, with everything needed to erectit attached, ensuring that parts aren’t lost during storage, transportor deployment during bad weather.

Each AquaFence element consists of two boards of marine gradeplywood in compact flat packs. A standard AquaFence element is2m long and constructed to tolerate water heights from 60cm to120cm, although custom elements are made to order.

Once an element is hand-lifted into place, it is a case of raisingthe vertical section, which forms the wall, and clipping four secur-ing poles into place. The next element is then attached and a highlydurable, PVC section that is impervious to water ensures completeintegrity at the join. This method also enables a 5˚ angle to beimplemented (vertical and horizontal), which allows an AquaFenceflood barrier to follow an uneven course and to lessen the require-ment for specially designed elements.

When flood water arrives, the downward pressure of the wateron the bottom section of the element provides strength and stabil-ity ensuring that the AquaFence elements stay in place. This newconcept in flood protection has been developed to ensure highintegrity throughout an AquaFence installation, which is fortifiedby a specially developed seal that mitigates water ingress betweenAquaFence elements and the ground. In areas where there is a riskof heavy floating debris, a specially designed debris shield can befitted, which uses the flood water itself as a protective cushion.

AquaFence is available as a mobile version for hard ground instal-lation. The semi-mobile solution for soft-ground installation requiresthe use of a pre-fabricated concrete base. AquaFence engineers canwork with customers and contractors during the assembly of thebase which, due to its small size, is low-cost, inconspicuous andunobtrusive, allowing clear passage for pedestrians and vehicleswhen not in use. AquaFence can be used without this foundationbut it is recommended to use it for known flooding hotspots.

On average, a 200cm wide, 120cm high sandbag wall costs thesame as an identical sized AquaFence element. However,AquaFence can be used over and over, whereas sandbags may beused only once – they may become contaminated during floodingand are thus classed as hazardous waste and have to be disposedof as such, which is an expensive and time-consuming process.

AQUAFENCE IN ACTION

AquaFence is already used at several locations throughout Europeand is currently undergoing certification to the FM Global stan-dard in Hamburg. Norwegian insurance company Gjensidige haspurchased AquaFence and installed it outside a division of theNorwegian State broadcasting company NRK. NRK’s offices aresituated on the Myren estate near the river Aker in Oslo, Norway.Gjensidige decided to buy the AquaFence solution after a series ofepisodes where the river Aker broke its banks and water penetratedthe neighbouring building complex.

Another Norwegian customer is the Skedsmo Kommune, closeto Lillestrøm in Norway. In cooperation with NVE (the NorwegianWater Resources and Energy Directorate) Skedsmo has chosenAquaFence for protection from floods and high waters on the riverØyern. When the dike was built around the city, it was lowered inplaces to keep the view. In order to do this, NVE demanded thatalternative protection was made available, leading to the deploy-ment of AquaFence at a 140m section in front of Dynea Factory.

AquaFence has local offices in Rakkestad in Norway, Düsseldorfin Germany, and Washington, US. The company has also openednew offices in Stockholm in Sweden and in Warwickshire, UK.AquaFence UK will act as a central point of contact for AquaFencecustomers to address their local flooding issues.

The AquaFence UK office joined forces with AquaFence A/S todemonstrate AquaFence at the Tees Barrage during September,October and November 2007. A single AquaFence element wasplaced directly in front of the Bear Trap water gate to demonstratethe kind of pressure that AquaFence is able to cope with and alsoa longer section running parallel to the water flow, protecting twoislands from the water. As the water rushed by, the AquaFence ele-ments mitigated any water ingress into the protected area.

AquaFence is the brainchild of Thor Olav Rørheim. Since 1997,he has worked on development and improvement of flood pro-tection systems in cooperation with the Norwegian University ofLife Sciences (UMB) and Innovation Norway – with additionalsupport from the Norwegian Water Resources and EnergyDirectorate (NVE). This venture led to the establishment ofAquaFence in 1999.

www.aquafence.com

IWP& DC

On opposite page: Skedsmo Kommune has chosen AquaFence for protectionfrom the river Oyern;Left: Aquafence was demonstrated at the Tees Barrage, UK

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The Severn Estuary is of significance to nature conservation at thenational, European and international levels and so has been afford-ed corresponding degrees of legal protection. Designated as both aRamsar Site and Special Protection Area under the EU HabitatsDirective, it is also in the process of being designated as a SpecialArea of Conservation. The estuary also comprises a series of Sitesof Special Scientific Interest.

SDC’s chairman, Jonathon Porritt, said: “We are excited aboutthe contribution a Severn barrage could make to a more sustainablefuture, but not at any cost. The enormous potential for a Severn bar-rage to help reduce our carbon emissions and improve energy secu-rity needs to be balanced against the impact on the estuary’s uniquehabitat as well as its communities and businesses.”


FIRST mooted in 1849, proposals to construct a tidal bar-rage across the Severn Estuary to link south west ofEngland with Wales have entertained generations ofwould-be developers. This mega project could generate

5% of the UK’s electricity needs, and would be equivalent to thesame level of output as about two conventional 1GW power sta-tions. Advocates of the scheme believe it will be a major step indelivering renewable energy.

With a potential capacity of 8640MW and an estimated outputof 17TWh/yr, the Severn barrage has been described as a vision-ary project, unparalleled in scale. Reports also state that it wouldprovide ancillary advantages in an area prone to flooding – therisks being highlighted in 2007 when large parts of the rivercatchment in the counties of Gloucestershire and Somerset wereinundated – though the benefits from the possible alleviation offluvial flooding and heavy rains would be minimal at best.Transport also features in the project concepts as the barragecould also potentially provide the basis for a new rail or road linkfrom England to Wales.

The last main push at examining a tidal barrage was in the1970s. Most recently, the Sustainable Development Commission(SDC), which is the UK Government’s independent advisory bodyon sustainable development - was charged to address tidal power,particularly in the context of a Severn barrage - published a reportin October 2007 supported by an array of research reports. Black& Veatch (B&V) prepared one of the evidence-based researchreports (No 3 - “Severn Barrage Proposals”)[1] .

SDC came out strongly in favour of a barrage scheme. It saidthe Government should seize the ‘unique opportunity’ and pressahead with the project that would help the UK meet its carbonreduction goals, provided it could be shown to meet toughtargets under EU environment laws.

Renewed promise for Severn powerTempted by the promise of a major long-term supply of renewable power, the UKGovernment is looking seriously, again, at proposals for a tidal barrage across theSevern Estuary. Report by Suzanne Pritchard

TIDAL

Cardiff

Weston-Super-Mare

Barry

Bristol

Cardiff-Weston Barrage

Shoots Barrage

M4M4

M5

River Usk

RiverW

yeRiver Avon

Figure 1 – Layout of the Cardiff-Weston Barrage and Shoots Barrage

Cardiff-Weston vs Shoots –a comparison of thebarrage schemes

Cardiff-Weston barrage The Shoots barrage

Length of barrage 15.9m 6.5m (approx)

Turbine No x runner dia. 216 x 9m 30 x 7.6m

Type of turbine Bulb, fixed distributor, Straflo or rim generator,variable runner blade variable distributor, fixedangle runner blades

No of turbines/Caisson 4 2

Generator capacity 40MW 35MW

Total installed capacity 8,640MW 1,050MW

Annual energy outputwith reverse pumping 17TWh (Approx) 2.75TWh

Annual energy, ebbgeneration only 16.5TWh(approx) 2.75TWh

Contribution to UKelectricity supply(2006 data) 4.4% 0.7%

Capital cost (2006) £15B £1.4B-£1.8B

Annual O&m costs £115M £22M-£27M

Unit cost of electricity 3.6-22.3 p/kWh 3-15.4 p/kWh

Annual saving in CO2based on 0.43kg/kWh 7.3M tonnes 1.2M tonnes

Lifetime carbon saving 877M tonnes 142M tonnes

Environmental aspects Both schemes need to fish passes and injurylook at sedimentation; injury passing through

turbines; and effects onwading birds.


TIDAL

SHORTLISTED

Studies have shown that tidal power barrage schemes with embank-ments of a minimal length result in significantly lower unit costs ofenergy than equivalent schemes with a longer embankment. Withthis in consideration, only two schemes shortlisted for inclusion inthe SDC study remain as the most likely to generate electricity at anacceptable cost. These are the Cardiff-Weston and Shoots projects.

The Cardiff-Weston scheme is a proposed barrage betweenLavernock Point, west of Cardiff, and Brean Down, south west ofWeston-Super-Mare. It will operate as an ebb generation schemebut with the ability to use the turbines as pumps at around the timeof high water to increase the amount of water stored in the basin.By pumping at low head, and generating later at relatively highhead, a net increase in energy is obtained.

As the bigger of the two options, Cardiff-Weston would stretch16.1km across the mouth of the estuary, cost an estimated £15B(US$30B) to construct and produce approximately 8.6GW ofpower. It is being developed by a consortium of contractors andmanufacturers called the Severn Tidal Power Group (STPG), com-prising Sir Robert McAlpine, Balfour Beatty Major Projects,Alstom Hydro, Rolls Royce Power Engineering, Taylor WoodrowConstruction and Tarmac Construction.

A second, more modest, scheme that would be sited upstream,called the Shoots barrage, calls for a 4.1km long project. The pro-ject is estimated to cost only a tenth of the former option and pro-duce approximately 1GW of power, with an annual output ofaround 2.75TWh/yr. The proposal is basd on generating with flowfrom the basin to the sea, mainly during the ebb tide. The schemewas originally proposed during the 1920s and it is being developedby Parsons Brinckerhoff (PB) in response to the 2006 Energy Review.

These two schemes are considered to be the most prominent andwell-studied proposals for a Severn barrage and the SDC selectedthem for further study. They have been described as good examplesof potential projects in terms of scale, power output and potentialimpacts. The key technological aspects of the Cardiff-Weston andShoots barrages are examined below.

CARDIFF-WESTON BARRAGE

At the proposed Cardiff-Weston barrage, each of the 54 caissonswould house four 40MW bulb turbines with 9m diameter run-ners. A four-turbine arrangement is the preferred choice as test-ing showed overall economy and improved stability when oneturbine water passage has to be dewatered for maintenance. Eachpassage can be closed off by inserting stoplogs from the deck,which allows for easy access to the entire area for inspection andmaintenance. Similarly, stoplogs or “limpet” gates would beinstalled in all four water passages for each caisson being floatedinto position during construction.

After installation, most of the cells would be filled with concrete

or sand to increase stability of the cellular structure caisson and pro-vide added mass in the event of ship collision.

A 350 tonnes capacity crane, spanning a service road and theaccess openings above the turbine-generators, would provide thelifting capacity for maintenance of the mechanical and electricalequipment. An elevated dual carriageway road on pillars wouldprovide a public road crossing of the estuary and the route for thepower cables.

STPG proposes wants the turbine caissons built in several con-struction yards in the UK and, possibly, in mainland Europe.Building would take place in a dry dock and would be completedalongside a quay after the dry dock had been flooded and the part-complete caisson floated out. Each caisson would set down near thebarrage, attached via two winch pontoons to a number of mooringlines, refloated and winched into final position.

The consortium has also favoured a Kapeller turbine-generatorwith four variable-angle runner blades with a fixed distributor. Themain features of the arrangement is:• No. of installed machines: 216.• No. of machines in each control group: 24.• Machine type: Kapeller.• Runner diameter: 9m.• Speed: 50rpm.• Generator rating: 40MW @ 0.9 power factor.• Generator terminal voltage: 8.6kV.• Total installed capacity: 8,640MW.• Transmission links to shore: 400kV.The number of turbines required and the difficulty of assemblingsuch numbers quickly in a pronounced tidal environment have ledSTPG to conclude that the turbines and generators should be pre-assembled as complete units onshore but not placed in caissonsbefore float-out as that could cause the construction programmeto extend unacceptably. Instead, when required, they would betransported two at a time by barge and off-loaded into position bya heavy-lift barge crane. The weight of each unit would be around2,000 tonnes, well within the capacity of existing cranes.

During construction of the embankment for the barrage, an ini-tial mound of rockfill on the seaward face would be built to gaincontrol over the tidal flows and protect subsequent work on thebasin side. The rock size required at any place would depend on themaximum current to be expected across the part-complete embank-ment. The design of the embankment would also include:• A core of hydraulically-placed sandfill, protected from currents and

small waves on the basin side by successive containment moundsof quarry waste or other cheap fill of suitable size particles.

• Filter layers between materials of different sizes to prevent migra-tion of finer materials into coarser materials.

• Armour layers to provide permanent protection against wave attack.• A wide crest to accommodate the road and the main power cables.

Rockfill Embankment

Rockfill EmbankmentSluice gates

Turbine caissons

0 1 2km

Navigation lock

Figure 2 – Location of the Shoots barrage proposal


TIDAL

The initial rock mound would have slopes of 1V:2H, which would besuitable for a hard seabed or where the seabed material is sand orgravel. On the English side of the estuary, the embankment would haveto cross deep, soft sediments. A flatter slope may be required to pre-vent slip failures.

STPG believes that the Cardiff-Weston barrage could be builtwithin five to seven years, depending on the number of work yardsprovided for construction of the caissons.

THE SHOOTS BARRAGE

The design of the turbine caissons for the Shoots barrage option isbased on the use of the “Straflo”, or rim turbine-generator, with a7.6m diameter runner and two turbines to each caisson.

Above each pair of turbines there would be a 32m wide sluice,which would be much higher than the equivalent level for theCardiff-Weston barrage, where the sluice gates would be fully sub-merged. PB has selected this level partly to help minimise the amountof silt carried into the basin.

Above the sluice water passage, on the basin side of the caisson,would be a continuous building which would house a travellingcrane to service the turbines, turbine ancillary equipment andelectrical equipment.

PB has based its cost estimate for the Shoots barrage on the use ofconcrete caissons. However, it points out that the caissons could bemade from steel, which would permit the use of existing constructionfacilities in different parts of the country. If concrete was to be the con-struction material, the greater draft of the caissons compared withsteel caissons would require a purpose-built construction yard.

The arrangement of the Shoots barrage includes sluices above eachpair of turbines, except for two caissons adjacent to the ship locks.This would provide 13 sluices. Each caisson would have a 30m wide

counterweighted radial gate. Additionally, there would be foursluices in caissons without turbines.

The embankment for the Shoots barrage would be built outsidethe deep water channel, on the shoulders of the estuary, and there-fore is seen to present less of a construction problem than theembankment for the Cardiff-Weston barrage. PB plans for theembankment to be constructed in 3m lifts, with the outside facesprotected by mounds of adequately sized rockfill to resist the max-imum current flow at the time. Between the protection moundswould be a core of dredged sand fill with suitable filters between thesand and the protection mounds. The seaward slope would be pro-tected by an armoured layer of rocks weighing 2 tonnes, and thebasin slope with smaller material. This permanent slope armouringwould be added as construction progressed, again to minimise theamount of partially completed embankment exposed to current andwave attack.

The electrical and mechanical equipment design for the Shootsbarrage is at a preliminary stage of development compared with theCardiff-Weston barrage, but PB puts the installed capacity of each“Straflo” unit at 35MW – less than the rival options due to thesmaller tidal range at the proposed site. There would be a total of30 machines, giving an overall capacity of 1,050MW.

PB believes Shoots barrage could be constructed and be readyfor commissioning in about four years, with the fabrication of 21caissons being completed within two years and all caissons placedin position three years after the start of construction works.Closure of the barrage would be achieved by raising the embank-ments above high-tide level while keeping the turbine and sluiceopenings clear to minimise flows over the partly-completedembankments.

Both barrage options would provide variable, but predictable,supplies of electricity to the transmission grid. The current plannednetwork should have enough capacity for a barrage the size ofShoots without requiring significant network reinforcements.

2 sluices

LavernockPoint

FlatHolm

SleepHolm

80 sluices 74 sluices168 turbines

15.9km

48 turbines

Elevated road

Shippinglocks

+67

+21+11 +15

Rockhead

N

Sluices

Sluices Sluices

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BreanDown

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Locks

10

20 20 2020

40

40

20

20 20

20 20 20

10

3030

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Figure 3 – Layout for the barrage for the Severn Estuary as proposed by STPG


TIDAL

However, the larger Cardiff-Weston scheme would affect thewider system and necessitate a more detailed study of transmis-sion needs. A split connection, sharing capacity between the trans-mission network on the north and south sides of the estuary, islikely to be needed.

The most recent report on financing the schemes, concludedin 2002, said that it was possible to envisage the Cardiff-Westonbarrage being financed by the private sector. Such financingwould be subject to the necessary policy instruments to achievelong-term security of supply contracts, and with capital grants torecognise the value of non-energy benefits. For the smaller Shootsscheme, though, it is anticipated that there may be sufficient inter-est not to require intervention.

THE TIDAL LAGOON ALTERNATIVE

The Severn barrage schemes are expected to be the principal focusof a new feasibility study into harnessing power from the waters ofthe Severn Estuary. Ministers and officials at the UK’s departmentsfor Business, Enterprise and Regulatory Reform (DBERR), andEnvironment, Food and Rural Affairs (Defra), and other keybranches of Government are drawing up terms of reference for whatis expected to be the most comprehensive study of the estuary’s tidalenergy potential. The study itself is expected to take at least 18months to complete and its conclusions will not be made publicuntil the autumn of 2009 at the earliest.

A serious alternative likely to feature in the feasibility study is

With support from some high profile politicians, including former Prime MinisterTony Blair, the Severn barrage has sprung into the public consciousness yetagain. There’s a déjà vu sense of awareness of this latest rise to politicalprominence. First mooted as far back as 1849, the construction of a barrieracross the Severn Estuary, linking south west England with Wales, entertainedwould-be developers throughout the 1970s, 80s and 90s. This mega-project,that could generate 5% of Britain’s electricity needs, has rebounded inresponse to the nation’s rallying call for clean, secure and reliable supplies ofpower from renewable sources.

And it is speculated as unlikely, even if a go-ahead were to be given to theconstruction of a barrage, that such a structure would be finished in time tocontribute significantly to the Government’s – and Europe’s – much vauntedambitions for a major contribution to power supplies from renewables by 2020.

Despite a history of on-off deliberations, the scheme’s latest renaissance hasgalvanised the various combatants in the Severn barrage debate yet again. Thoughwearied over the many years by claim and counter-claim on its environmentalimpact in an area renowned as a haven for birds and marine life and frustrated bydashed hopes, detractors have been urged by the Secretary of State for Businessto ‘open their minds’ on the future of a barrage.

A Severn barrage would harness the power of the estuary using the proventechnology of a hydro-electric dam, but filled by the incoming tide rather than bywater flowing downstream. The project’s potential to provide 5% of total UKelectricity demand from renewable, British sources will be examined alongside theimpact on the natural environment, and social and economic aspects, as well asfinancing. The study will also look at the potential for other UK barrages. InSeptember 2007, the Secretary of State for Business said that the Government wasdetermined to ‘drive forward with delivering a step change in [the] use of renewableenergy’, and added: ‘This is truly a visionary project, unparalleled in scale.’

A barrage would also require compliance with a wide range of environmentallegislation, including the EU Habitats and Wild Birds Directives.

SDC’s chairman, Jonathon Porritt, said that for this reason, the developmentmust be publicly-led as a project and publicly-owned as an asset, ‘in order toensure that the government takes full responsibility for taking a sustainable,long-term approach’. Speaking at the publication of the SDC report, theSecretary of State for Wales said the barrage was a a ‘trailblazer’ and could beas significant a development as the Channel Tunnel.

The Government commissioned the SDC to undertake an assessment of tidalpower in the UK. It has set ambitious targets for reduction of CO2 and theproduction of renewable energy by 2050 - a minimum of 60% reduction in CO2from 1990 levels with an interim target of 26-32% reduction. Currently, however,the nation produces just 2% of its energy needs from renewable resources and by2012 it will be 20GW short in electricity capacity when many existing nuclear andageing coal-fired power station reach the end of their working lives. At presentthere are proposals for 26GW of coal and gas-fired power stations to replacethem, if the current annual UK demand of 75GW is to be met.

But the main thrust of the SDC report outcomes is in the potential to generatepower from a tidal barrage. Its authors also cast their net farther afield, toconsider tidal stream sites in the Firth of Forth and Sutherland in Scotland, atAnglesey in north Wales, and in Northern Ireland. The tidal range resource inEngland is concentrated in the estuaries off the west coast including theMersey and Humber estuaries, as well as Severn.

Most notable during the last four decades have been a shortlist of majorprojects, the first of which was promoted through a study by the formernationalised Central Electricity Generating Board (CEGB), in 1975, for the

Secretary of State’s Advisory Council on Research and Development for Fueland Power. But any notions of a barrage were swiftly dismissed on thatoccasion, as it came in an era of cheap oil and was deemed to be unviableunless the energy situation deteriorated significantly.

Fortuitously, perhaps, just such deterioration emerged from the revolution inIran and the ensuing oil shock, and a Severn Barrage Committee, under SirHermann Bondi, investigated the CEGB’s findings in 1981. Six possible barragelocations were revisited, including one that remains close to that most popularto this day – a concrete powerhouse between Brean Down and Lavernock Point,featuring sluice and plain caissons together with sand and rock-filledembankments. Three years later, Wimpey Atkins proposed a smaller barrage atEnglish Stones. Another three years passed before that same scheme wasrevised to better tackle the issue of silting in the estuary and it, too, wasfurther updated in 2006 to become known as the Shoots barrage.

In 1989, the Severn Tidal Power Group (STPG) built on the work of the SevernBarrage Committee, confirming the Brean Down-Lavernock Point location as afavoured site for such a structure, but suggested that the power output might beboosted to somewhat more than originally envisaged – not 7.2GW, but 8.6GW.The barrage would use existing technology, as used in the Rance tidal barrage inFrance, built 40 years ago and which today still produces 250MW.

Building the STPG structure would entail the construction of an array of sluicesto let in the tide and which would then be closed to force the waters through atotal of 216 x 40MW turbines. Shipping would be allowed to pass through thestructure by a system of locks designed to handle the largest containervessels. It was estimated that construction may take about eight years,employing some 35,000 workers at its peak, and the minimum lifespan of thebarrage would be 120 years.

But it was not to be. The Government of Margaret Thatcher shelved the plans asan emerging environmental lobby strengthened its influence on home affairs. Itwas not until climate change concerns gained major significance inenvironmental politics, coupled with soaring oil, gas and other energy costs, thatthe economics of the barrier became much more favourable. The advent ofrenewable energy discounts under the Renewables Obligation for “green”sources of energy, lower interest rates impacting on the cost of loans, and long-term financing of massive infrastructure projects all now combine to make majorschemes such as the barrage more viable and attractive. Consequently, therehave been renewed calls for these plans to be re-appraised.

If the tides of the Severn are to be tamed, neither a barrage nor lagoons arewithout benefit or disadvantage. The Government’s studies will doubtlessattempt to address them all. But there are signs that the public’s uncertainty -or sheer antipathy - for such a scheme may be softening. Initially, the SDC’spublic and stakeholder engagement programme, published previously, showedthat after being given summary information on a barrage proposal, including thepotential advantages and disadvantages, 58% of people across the UK were infavour of a barrage and 15% against. This support was mainly because of theperceived climate change benefits. Electricity from a barrage would displaceoutput from fossil-fuelled power station, making a significant contribution to theUK’s renewable energy targets.

More importantly, perhaps, is the considerable political weight of those inGovernment being put behind a barrage. Even the celebrated scientist and “Gaia”theorist, James Lovelock, has added his name to those backing the scheme.

The Severn barrage debate looks set to entertain for some time to come.

Severn Barrage revisited


TIDAL

the preferred choice of environmental campaigning organisationFriends of the Earth (FoE), which has proposed its own planbased on the concept of a series of tidal lagoons. These man-madestructures would be built in the estuary to both fill and drainthrough turbines, generating power for the grid. Consisting ofrock-walled impoundments, they would cover an estimated areaup to 60% of that affected by a barrage, but their smaller con-figurations would not impound water in the ecologically sensi-tive inter-tidal areas of the estuary. As lagoons could besub-divided, power could be generated at more states of the tidethan would be the case for a barrage. The result would be a lowerpeak output but considerably lower construction costs.

However, lagoons are by no means a win-win solution to gen-

erating power from the Severn tides. They would require consid-erably more construction aggregates than a barrage and there couldbe significant environmental and social implications in sourcingup to 200M tonnes of rock, sand and gravel, it is estimated.

Tidal lagoons are not a new concept but is as yet unproven due touncertainties over design, construction methods and physicalimpacts. In the absence of sufficient evidence to assess the long-termpotential of tidal lagoons, SDC believes it is in the public interest todevelop one or more demonstration projects in the UK to carry outthe much-needed research.

OPPORTUNITY

SDC believes that there is a strong case to be made for a sustainableSevern barrage on a publicly-led, publicly-owned basis to ensure sus-tainability. It does, however, caution the Government about theimplications of its decision regarding the construction of a Severnbarrage and calls for analysis to show whether a true environmen-tal opportunity is being presented. If compliance with EU environ-mental directives is found to be scientifically or legally unfeasible,then proposals for a Severn barrage should not be pursued, it says.

If the tides of the Severn are to be tamed, neither a barragenor lagoons are without benefit or disadvantage. The Government’sfeasibility study will no doubt attempt to address them all.

Additional reporting by Chris Webb

Reference1. Sustainable Development Commission (SDC). “Tidal power in the UK -Research Report 3: Severn barrage proposals; an evidence-based report.”Black & Veatch. October 2007.

IWP& DC

Other Severn Barrage proposalsThe Sustainable Development Commission (SDC) carried out acomprehensive study of tidal power in the UK as part of the Government’slatest review of energy policy. Five research reports were commissioned andlooked at UK tidal resources; tidal technologies; case studies; and a reviewof non-barrage and barrage proposals for the River Severn.

Research Report No 3 looked at various proposals for the Severn barrage. Itwas an evidence-based report with Black & Veatch as the lead consultant.Other members of the project team included:

• Clive Barker: sub-consultant on technical and modelling issues.

• ABPmer: sub-consultant on environmental and social impacts.

• IPA Consulting: sub-consultant on economics.

• Econnect Consulting Ltd: sub-consultant on grid implications with assistancefrom Graham Sinden of the Environmental Change Institute, Oxford.

As well as the Cardiff-Weston and Shoots barrages, six other barrage-basedschemes were short-listed for inclusion in the study:

• Hooker scheme: A barrage located near Shoots with a second basinseaward. The barrage would operate in ebb generation mode and thesecond basin could be operated out of phase with the barrage, during theflood tide or in phase as ebb generation mode. This scheme was originallyproposed by A V Hooker of W S Atkins, Cardiff, in 1977.

• Minehead-Aberthaw scheme: A barrage on this alignment, often referredto as the “outer barrage”, has been identified as the location where themaximum energy potential of the estuary could be developed.

• Cardiff-Weston scheme with second basin: A barrage similar to theCardiff-Weston scheme, operating in ebb generation mode, with a secondbasin on the English side of the estuary. This second basin would bedesigned to operate in flood generation mode. This scheme was developedto provide a method of utilising nearly the full energy resource in theestuary, about 23TWh/year, rather than pursue a very large “outerbarrage” seaward.

• Shaw two-basin energy storage scheme: A barrage similar to the Cardiff-Weston scheme and also with a second basin seaward. However, thesecond basin, equipped with deep-set pump turbines, would have its waterlevel below minimum tide level at all times so that power could begenerated at times when the main basin was unable to do so. This wouldresult in the scheme having a large element of pumped storage built in,and a significantly better firm power capability than the barrage alone. Thisscheme was originally developed by Dr T Shaw, then of Bristol University.

• Dawson continuous power scheme: A barrage across the outer estuary,near Minehead, equipped with two sets of sluice gates and ship locks.Between the gates, an embankment connects to Brean Down, near Weston,forming a second basin. The main basin is filled through one set of sluices;the second basin is emptied through the other set. Power is generatedwhen water flows from the main basin to the second. By keeping the waterlevel in the main and second basins within the upper half and lower half ofthe tidal range, respectively, continuous power can be generated. Thisscheme is proposed by R Dawson of Dawson Construction Plant Ltd.

• Severn Lake scheme: A barrage in about the same location as the Cardiff-Weston scheme but about 1km wide and including two wave farms on theseaward side, four marinas and other features not directly associated withenergy production. This scheme has been proposed by the newly-formedSevern Lake Co Ltd.

From top to bottom: Construction of the barrage caissons as shown in the STPGproposal. Ebb tide turbine operation, as envisaged by the STPG proposal

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IWP&DC - 2008-03.pdf