__ ALASKA POWER AUTHORITY.. . PUBLIC PARTICIPATION OFFICE___ 333West4th-Suite31., . . Anchorage, Alaska 99501~ (907) 276-0001

•e sUSltna

•lesSeptember 1981

•NI

III•II1.:\"",.,

I.!ntain and Denali faults arenownIts.

inch equals 13.3 miles

CASTLEMOUNTAINFAULT

"Talkeetna. For the Susitna project all faults and lineaments (possible faults)

within 100 km (62 miles) of either dam have been complied frompublished and unpublished reference materials, satellite 1m·agery, radar Imagery,nlgh·altltude aerial photography, and lowaltitude aerial photography.

Based on this work, the only faults In the North American Plate

within approximately 62 miles of the dams which are judged tobe active are the Denali fault and the Castle Mountain fault.

Beneath the upper 15 to 20 miles of the earth's crust is theBenioff Zone. This is also an aptive fault zone. The depth to theBenioff Zone beneath the Susltna dam sites is about 34 miles.

Source:Interim Report on the Seismic Studies for (the) Susitna Hydroelectric Project, December 1980,

prepared by Woodward-Clyde Consultants for Acres American, Inc. and the Alaska PowerAuthority.

5. At present, the 13 features are not known to be faults with re­cent movemenUfpresent studies show any recent move­ment, then the potential for surface rupture through eitherdam site and the ground motions associated with earth­quakes on the fault will need to be evaluated.

4. Within the site region, 13 faults and lineaments (potentialfaults) are receiving additional study in summer 1981 to betterdefine their potential effect on dam design. Four of thesefaults and lineaments are near the Watana site and nine are inthe area of the Devil Canyon site.

6. Preliminary estimates of ground motions at the sites weremade for the Denali and Castle Mountain faults and theBenioff Zone. Of these sources, an earthquake of magnitude8.5 occurring within the Benioff Zone would create the max­imum ground shaking at the dam sites.

Preliminary Closest Distance of FaultMaximum Credible to Site (miles)

Earthquake Magnitude Watana Devil Canyon8.5 43 407.4 65 718.5 31 37

FaultDenaliCastle MountainBenioff Zone

The following are the preliminary seismic conclusions.

2. The known faults with recent movement are: the Denali fault(north of the sites), the Castle Mountain fault (south of thesites) and the Benioff Zone (about 34 miles beneath the sites).

3. The closest distances of these faults from each site and thepreliminarY maximum credible earthquake magnitudes for thefaults are the following:

This issue gives information about the seismicity of the upperSusitna River basin and discusses the question of building safedams in seismic areas.

1. No faults with known recent movement (movement in the last100,000 years) pass through or near the proposed Susitnadam sites.

)reliminary findings:Available on Susitnalasin seismicity

2 thesusitna hydro studies/september 1981

Alaska is part of a large continental landmass (the North American Plate) which lies adjacent to anoceanic mass (the Pacific Plate). The Pacific Plate is moving northwest at a rate of about 2 inchesper year.

»'(")r\»» z(fl »"'\0»»

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To date no active faults have been identified inthe Talkeetna Terrain itself. Studies in 1981 arefurther evaluating 13 faults and lineaments (potential faults) in the vicinity of the Watana andDevil Canyon damsites to determine whether or not the faults and lineaments may be active.One of those receiving additional study is the Talkeetna Thrust Fault.

E?·z e>

cur at the point on the One is a magnitude 8.5 The Susitna dam sites liefault closest to a proposed earthquake on the Denali within a region that isproject, such as a dam fault, 40 miles from the believed to be relativelysite. dams; the other isa stable. This region is

magnitude 8.5 earthquake known as the TalkeetnaIt is based on geological in the Benioff Zone, about Terrain.and historical data, and is 34 miles below the surfaceusually of a magnitude of the earth at the dams. The boundaries of the Ter-greater than historical rain are the Denali fault,earthquakes. 6. How much ground shaking the Castle Mountain fault,

would that cause? and the Benioff Zone4. How reliable is it? (which is about 34 miles

The Maximum Credible The ground shaking that below the surface of theEarthquake is considered would occur at the dams earth). These are all activeto be a reliable parameter from a magnitude 8.5 fault areas;to use for dam design. earthquake on the DenaliThere are over 11,000 fault is considered to have Energy release appears todams worldwide. Some of an average peak accelera- be occurring primarilythese have been built in tion of 20%g. along the boundaries ofmoderate to high seismic the Talkeetna Terrainareas such as Oroville dam The ground shaking that rather than within it.in California and several would occur at the damsdams in the San Francisco fromamagnitude 8.5 Within the Terrain, noBay Area along the San earthquake jnthe Benioff evidence of activefaultsAndreas fault. Zone is considered to have has been observed. Sorne

anav;eragep~ak accelera- earthquake activityisgc-Several dams have been tion of 40%g. curring and has occurreddamaged during earth- within the Terrain,but thequakes, such as Koyna in 7. How does thatcompareto earthquakes are typicallyIndia and Hsinfengkiang in the 1964 earthquake? small to moderate in size.the People's Republic ofChina. This damage was As a comparison, the To date no active faultsduein large part to the average peak acceleration have been identified intheabsence of design con- estimated at Susitna Talkeetna Terrain itself.siderations for reservoir- would be 1/3 to 1/2 as Studies in 1981 are furtherinduced seismicity. much as the average peak evaluating 13 faults and

acceleration estimated at lineaments (potential5. What are your estimates Valdez during the 1964 faults) in the vicinity of the

for the largest earth· earthquake. Watana and Devil Canyonquakes that could occur in damsites to determinethe area of the proposed 8. Just how seismically ac· whether or not the faultsdams? tive is the area where the and lineaments may be

proposed dam sites are? active.

This 2 inches ofmovement gets absorbed along a feature in the Gulf of Alaska called the AleutianTrench. Her~ one plate is thrust below the other(iri a process called subduction) as shown in thediagram. The zone ofseismicity associated with the subduction is referred to as the Benioff Zone.

Earthquakes can occuralong the·Benioff Zone where the two plates are in contact. This is wherethe 1964 earthquake occurred as shown in the diagram.

Earthquakes are also caused within the plates themselves. Movement of the plate causes stressesto buildup and the energy is released by rapid movement along planes of weakness (faults).

•The following are responses tofrequently asked questions.The information wasdeveloped by Jon R.Lovegreen, Senior ProjectGeologist, Woodward-ClydeConsultants.

1. Do earthquakes occur onlyalong faults?

No. There are four generalcategories of earthquakes.These categories are col-

Lovegreenlapse earthquakes,volcanic earthquakes, ex:.plosion earthquakes, andtectonic earthquakes.

Tetonic earthquakes arethe most common type ofearthquakes and are theearthquakes pertinent tothe design of the Susitnaproject.

Tectonic earthquakesresult when stresseswithin the earth builduptothe point thatthe strE3ngthof the rock is exceeded.Relatively instantaneOYsre.lease ofstrainen~rgy

take~.pICice. along·az()n.~

ofV>'~Cikness.l"he energyrelease·caus~sthE3 g~()u~d

shaking ()fth~~artrg~Ci~~and the zone ofweaknessisthefault.

2. .H.?\V do you ensure. that)'?l;I·ar~ i~~n!H)'ing.".i~ual.lyall.sour9~.s?!(f:lar.th.qU~kesthatcouldaffect

the dam?

The identificatiOn ofs()~rcesfQr·~Cirthquakes.inAlaska is based on ex-periengeWith faults andearthquakes in Alaskaandworldwide. From this ex-perience, it is possible tornCikejudgements aboutth~pote~tial sources ofeartrguakes in a regionsuch as the TalkeetnaMountains. Thesejudgements do not ensurethat all sources are iden-tified, rather, thejudgements identify allsources of earthquakeswhich experience hasshown could be possible.

For large projects such asthe Susitna hydroelectricproject, a conservative ap-proach is used. This ap-proach includes the studyof faults which are onlyremotely possible sourcesof earthquakes.

The past experience of thefirm which is studying thefaults and earthquakes(Woodward-Clyde Con-sultants) includes ex-amination of active faultsand earthquakes inAlaska, California,Nevada, Utah, Central andSouth America, Europe,Africa, the Middle East,Australia, New Zealand,and Japan.

3. You use the term "max·imum credibleearthquake." What is that?

A Maximum Credible Ear-thquake is considered tobe the most severe earth"quake associated with afault and is assumed to oc-

the susitnahydrostudies/september1981 7

Background information on proposed<Sus tna project

IIIIIIIIII

"\... ,...- ... ......

The Susitna hydroelectric pro­ject as currently proP9sEH:lin­volves two dams and reser­voirs on the Susitna River inthe Talkeetna Mountains ofsouthcentral Alaska.

The.project area is about 50miles northeast ofTalkeetna,Alaska and 118 miles north­northeast of Anchorage,Alaska.

The upstream dam, Watana, is

proposed to be developedfirst. It is currently being con­sidered as an earth/rockfilldam, approximately 880 feethigh. This would make it thefifth highest dam in the worldand the highest in NorthAmerica. It would impound a54-mile-long reservoir.

The downstream dam at DevilCanyon is currently being con­sidered as a concrete archdam approximately 635 feet

high. It would impound a28-mile long reservoir.

These dimensions'are approx­imate and subject to changeduring detailed design.

The feasibility study is beingmanaged and conducted byAcres American, Inc. for theAlaska Power Authority. Thestudies conducted to daterepresent the first year of aplanned two-year study (1980

and 1981). A draft feasibilityreport detailing research ef­forts in 10 different areas in­cluding economics, engineer­ing, and environmentalaspects of the proposed powerproject is due in March nextyear.

How proposed Heightabovelowest Rated Rated Year of

Susitna projects Year River State lounda- Crest Reservoir capacity capacity initialcom· or Nearest or Dam tion length capacity now planned opera-

Name ,pleted' Basin city Province Country type m m m3 x 10° (MW) (MW) tion

compare with 'Bonneville 1943 -Columbia Portland Oregon-Washington USA concrete 32 277 588 1,076 1938gravity

existing dams 'Glen Canyon 1964 Colorado Page Arizona USA concrete 216 475 33,305 1,021 1,431 1964arch

'Grand Coulee 1942 Columbia Coulee City Washington USA concrete 168 1,272 11,795 7,460 10,830 1942gravity

"'Hoover 1936 Colorado Boulder City Nevada-Arizona USA concrete 221 379 36,703 1,345 1,345 1936arch/gravity

°Mica 1973 Columbia Revelstoke British Columbia Canada earthl 245 792 24,670 1,736 2,610 1976rockfill

·Oroville 1968 Feather Oroville California USA earth 235 2,316 4,299 679 679 1967

'Devil Canyon (Proposed) Susitna Talkeetna Alaska USA concrete 200 378 1,235 0 400 (Proposed)( 2000 ) arch ( 2000 )

·Watana (Proposed) Susitna Talkeetna Alaska USA earth/ 271 1,662 12,347 0 800 (Proposed)( 1993 ) rocklill ( 1993 )

Sources: 'Corps 01 Engineers, Portland, Oregon ") "Major Dams ot the World," T.W. Marmet,lnternalional Water Power ·Civll Design, Slate of California, Oroville. California'Western Area Power Office, Golden, Colorado. 4) and Oam Construction, Special Issue May 1981, Published by fPC 'Acres American, Inc., Anchorage. Alaska 1 Meter = 3.25 Feet

-) Electrlcal·Electronlc Press ltd., Ouadrant House. The Quadrant. -Acres American, Inc., Anchorage, AlaskaSutton, Surrey SM2SAS, England

Construction timed to match power demand

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Siage 3 - Devil Canyon400MW

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Siage 1 - Walana 400 MW

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2) the additional 400 MW ofcapacity at Watana is ready foroperation in 1995; and

3) the Devil Canyon dam with its 400MW is completed in theyear 2000.

1) The Watana damwith 400 MW would be completed in 1993,which is the earliest possible date because of time periodsinvolved in project evaluation, permitting, and construction;

Possible staging of Susitna project

This diagram shows how theSusitna development would bestaged under the medium forecast of future energy reoquirements.With this energy demand and ensuring that ade·quate generating reserves are maintained, power costs would beminimized if:

State [I]

ready to buy it. The energyconsumption forecasts pro­vi(jeestimateS"().fh()'Nmu~hpower can be sold in the yearsahead.

The Power Authority's ap­proach, then, is to postponespending money for the nextstage as long as possible toensure that there is the de­mand for purchasing the pro­ject's power. Money spent on aproject whose power cannotbe sold is money wasted.

Waiting too long to constructthe next stage, however, isunacceptable because therewould be an increasinglikelihood of not being able tomeet the peak demands. If thisoccurred, customers wouldhave to go witho~telectricityduring high use eriods. Thus,a balance has to e struck be­tween postponing additionalinvestments and ensuring ade­quate generation to meet peakloads.

Name . I I , , , I I I I I I I , , I I I I I I I

Mailing iii iii iii i I I I iii iii i I

AddressCity

3) the Devil Canyon damwithan installed capacity ofabout 400 MW.

2) an addition to the Watanacapacity of another 400MW;and

1) the Watana dam with in­stalled capacity of 400MW;

This staging prQ\li(j~ss91Tl~flexibility in the seq\J§pc:e.andtiming of construction. At thesame time, there are certainconstraints on thatflexibility.

Both the Watana capacity ad­dition and the DevilQanyonproject could be brought online earlier or atthe same time,if needed, while all threestages could be postponeddemand turned outto be lessthan anticipated.

Meanwhile,the balancing hasIn stagingtheSusitna.develop- to. be done in thel midst ofament, the primary.objective is great deal of unqertainty aboutto keep the cost of power as what the actual demand for10waspossible.Thisisdone power is going to be in theby minimizing expel1ditures future.Astirn§ gOEls 011 andwhile selling as much of the future power demandsavailable power as possible. become rnorecertain, the plan-But the power cannot be sold ned staging would be adjustedif there aren't consumers to suit actual conditions.

The proposed Susitna develop­ment is presently envi~,ioned

as having three distinctstages:

III

............................ _­I This public information document on the Susitna hydropower project was developed by the Alaska Power Authority

Public Participation Office, Nancy Blunck, Director. Comments on the substance of this newsletter and ideas forfuture pUblications should be forwarded to the Public Participation Office by way of the following coupon.

Last First Initialiii iii iii iii iii iii I i I

If you wantto get futurenewsletters

the susitnaihydrostudies/september1981 3

Three ways to measure the forceQfan earthquake

Accelerations Ol

«ion

'"Modified Mercalli Ole Ol

Intensity Scale '" c 'OOl &~" .~ §(1931. Wood and Neumann) Ol c.Q e;w.'!! .:;: (3 c ~

Ol-E e ~ '" on Ol0 ::;;§. cClu. w

I-1014 _

1. Detected only by sensitive I-instruments 1-2

l-I-

2. Felt by few persons at rest. I: 1015 _especially on upper floors;delicately suspended objects l-

I-may swing l-

I-3. Felt noticeably, but not I-

always recognized as earthquake; I-- 3 1016 _

I-standing autos rock slightly, I-vibration like passing truck

0.01g-l-I-

4. Felt indoors by many. outdoors by I--few; at night some awaken; I-

1017 -I-dishes, windows, doors disturbed; I-motor cars rock noticeably l-

S. Felt by most people, somet:'"4

breakage of ilishes. windows, l-I- 1018 -and plaster; disturbance of I-

tall objects50 I--I- 0.05g- I-

6. Felt by all, many frightened l-I-

and run outdoors; falling I-1019 -plaster and chimneys, I-- 5

damage small I-

7. Everybody runs outdoors; damage l-to buildings varies depending on l-

I--1020 -quality of constru?lion; noticed

200 I-by drivers of automobilesI-- 0.2g- l-

I-Panel walls thrown out of frames; I--

1-6fall of walls, monuments, I-chimneys; sand and mud ejected; I- 1021 -drivers of autos disturbed, 500 l-

I-- 0.5g - --9.• Buildings shifted off foundation, -cracked, thrown out of plumb; -ground cracked; underground - 1022 -pipes broken -I-- 710. Most masonry and frame t:structures destroyed; ground

600 t:cra?~ed; rails bent; .... 0.6g-pipes broken I-- 1023 -

11. Few structures remain standing; t:I-

bridges destroyed; fissures in I-ground; pipes broken, landslides, I-- 8rails bent I- 1024 --12. [)~!O~g~t()tal;lYaves seElllon ::gr~und surface; lines of sight I--and level distorted; objects I-thrown up in air I- 1025 _

9. How can there be no ac-tive faults in the area ofthe dam sites whenhistoric records showmany earthquakes occur-ring there?

In the area of the proposedSusitna dam sites earth-quakes occur within theNorth American Plate(which includes the upper15 to 20 miles oftheearth's crust) and in thePacific Plate (which is be-ing subducted, or drawndownward, beneath theNorthAmericanPlate).

Preliminary evaluation ofthe seismicity in thesetwoplates; wi,thintheTal,keet"na!errai~;s~ggest~thatmany ofthe~arthquakes,including IJirtually all ofthe moderate to largeearthquCl.kes.ar~.occurringin thePacific Plateatdep-thsof atleasf34 milesbeneath the dam sites.

Activity occurring in theNorth AinericanPlate isassociated'withenergyrelease on small faultplaneswhich'aretoodeepand too smallto causedisplacement altheearth~ssurface.

10. Why d()your studies notconsider faults that are in-active?

AII.faults and possiblefaUltsiwithihabolJt1 OOkm(62 miles) of theSusitnadam'siteshavebeenevaluated to determinewhether or not they are ac-tive faults: Those faultswhich have not haddisplacement in recent!:leoIO!:licitiinearecop~

sidered to be inactive.Faults which are inactiveare not important forseismicdesigri of,adambecauseearthqlJakes arenot expected to occuralong inactive faults.

11. Whatisc()nsideredanac"itivefault?

Various governinentalandregulatory agencies haVedefined activefaultsiinorder to assess the impor:tance of faults tothe

design of critical faci Iitiessuch as dams. Initiallythese definitions werebased on how recentlythere has been movementalong a fault.

For example, theUS.Bureau of Reclamationdefines a fault which hasmoved in the last 100,000years as active. The U.S.Army Corps of Engineersuses 35,000 years.

Recently there hasdeveloped an increasingconsensus that the activi­tyof afaUlt should be con·sidered by how often itmoves, how much move·ment is likely t()o~curand

what type ofmovementwill occur. From this inforc

mationthelikelihoodoffau It moveinenfcan"bemade and incorporated in·todain design.

12. When you refer to activefaults, how long a periodof time are you referringto?

As a guideline fortheSusitna project, AcresAmerican,lnc;hasdefinedan active fault as onewhich has had movement,or displacement;inthelast100,000years.

Pra~ml\:Reporton Seismic Studies for SusitnaHydroelectric ProJect, December 1980, pre­pared by Woodward·Clyde Consultants forAcres American, Inc. and the Alaska PowerAuthority.

In Anchorage, copies are available at theAlaska Resources Library in the FederalBuilding; at the University of Alaska Consor­tium Library; at the Arctic Environmelltalln­formation and Data Center; and at the Z.J.Loussac Library.

In Fairbanks, copips are available at the ElmerE. flasmuson Library, University of Alaska;and at the Noel Wien Library.

In Talkeetna, a copy is available at the Talkeet­na Public Library.

Modified Mercalli scaleThis scale.~erba"ydescribesthe effects of earthquakes.

AccelerationEngineers ofteriuse ac·celeration tOl11easure theseverity of earthquake mo·tions. The relationship of ac·celeration to magnitudemust include a considera'tion for the dIstance fromthe earthquake source.

fd!!gnitude and amount ofenergy releaseThese two columns showthat each increase inmagnitude (for example,from 5 to 6) is approximatelya 3Orfo!d increase in energyrelease.

Source:

Modified from Earth·Rock Dams. Engineering Problems ofDesign and Construction, J.L. Sherard, R.J. Woodward,S.F. Gizienski, W.A. Clevenger, John Wiley and Sons, Inc.,New York.

o4 the susitnahydrostudies/september1981

Designing Dams in Earthquake}}Gountry-An Interview With Dr. Harry Seed

Dr. H. Bolton (Harry) Seed, is a specialist in earthquake·resistant design and professor of civilengineering althe University of California, Berkeley, He also.serves on the Susitna ExternalReview Panel which is made up of six eminent engineers and scientists who provide independentreview of the Susitna hydroelectric feasibility study.

Dr. Seed has been a consultant on soil mechanics and seismic design problems since 1953. Overthe years, he has worked extensively with a variety of clients, including the U.S. Army Corps ofEngineers, the Executive Office of the President.ofthe United States,the World Bank, theFederal Power Commission,.BechteICorporation,Woodward,Clyde, the Metropolitan WaterDistrict ofLos Angeles, the Canadian Ministryofthe;Environment, and many foreign governmentagencies.He.has!,o~ked;or'!.about80dam.s1N.~~ld1Nid.eimostofwhich were in seismic areas.After adam ..failure in <::alifornia in the.~a~IY;?:~is,Dr.~eedauthoreddesign procedures for Califor·nia sot~atdam.failure.swo.uldnot happenagain;J;hese.procedures are now used throughout theworld to produce safe, seismic designs for dams.

Following are excerpts from an interview conducted by Nancy Blunck, Director of Public Par·ticipation, the Alaska Power Authority. The complete text is available upC:)O request.

QUESTION: What is your per­sonal experience with damdesign?

SEED: Since I am a specialistin earthquakes, I tend to get in­volved more with dams inhighly seismic regions thanother areas. So, for example,I've worked ona lot more damsin California than with dams inTexas or Florida, which arenonseismic regions. My ex­perience includes the designof perhaps 80 d~ms-50 or80dams for earthquake. problemsof one kind or another. Isuspectthatl ha"e.\o\'()rked onmore earthquake problemsrelated to dams than anybodyelse in the world.

QUESTION: What about thequestiopgfb~iWing safe dams.in aseismic area?

SEED: First of all,it is comforFing that at the present level ofknowledge ofthe.Susitna pro­jectthe intensity gf~hCiking

which can be anticipated ateither dam site is consideraply.Iessthan those in arl3asforlA/hichwe have already design­ed dams. Secondly, the peoplein Alaska should know thatdams have been·proposed tobe built in some extremelycritical areas.

QUESTION: What must damdesign in highly seismic areastake into account?

SEED: The firstthing in ahighly seismic area is to studythe dam site and find out ifthere is a fault in the founda­tiori ofthe dam or very close tothe dam. We prefer not to builddams directly over faults,although once in awhile wehave done that when there isno way to avoid

Even if you avoid the faultsin ahighly seismic region, thatdoesn't eliminate the problemofthe dam being subjected toextremely strong ground shak­ing in the eventofamajorearthquake...

So the second aspect of theproblem is to design the damto remain stable eventhough itis shaken by very. strong mo­tions from an earthquake.There are various ways inwhich that is effected. One isby controlling the materials ofwhich the dam is built. When Isay controlling them, I meanselecting materials which arecapable of withstanding earth­quakes better than others.Also, placing them in the damusing construction techniqueswhich enhance their naturalability, and providing a finish-

ed prpductwhich can safelywithstand the effects of theearthquake shaking.

The primary construction pro­cedure involved in placingearth materials in dams is incompacting the materiaUo ahigh enough density to make itstrong enough towithstandthe earthquake shaking. Thathas been done in many areas,but first you must carefullypredicttheeffects.of earth.;qlJake shaking on the dam andhow.dense the material needsto be to withstand a given levelof earthquake motions.

QUESIION:VVhatprojects areyou familiarwiththat resemblethe Susitna project?

SEED:Orpvill.~R~m!nc;~lifor.niais acobble and gravel filldam 700 feet high. Auburn damin California is a concrete damabout 600 feet high...TheUribante-Caparo project inVenezuela is a complex of fourdams and three powerhouses,with 400 to 500 foot high dams.The Alicura project in Argen­tina is a complex of threedams about 400 feet high.:.ThePueblo-Viejo dam inGuatamala is a rockfill dam500 feet high...And manyothers.

"I suspect that I haveworked on more earth,;quake problemsrelated to dams thananybody. else .intheworld."

QUESTION: Howdo these pro­jects resemble Susitna, andare there greater or lesserproblems?

SEED: The Oroville damis inCalifornia.The region in whichit was builtwassupposedlynonseisrnic, but in 1965 theyhad an earthquake very nearthe dam. So the designearth~

quake for Oroville isnow amagnitude 6.5 (onth~Richter

scale) earthquakepccurringdirectly under the dam site,which is a very strong earth­quake.

Oroville is about the sameheight as the proposedWatana dam and, as a matterof fact,was the one wesug­gested in our firstreport asprobably being the best modelfor that particular dam. I havebeen on the consulting boardfor that dam since it becamean earthquake problem, which

means having responsibilityfor determining the adequacyof the seismic design.

The Auburn dam in Californiais a hit'lhly controversial dam.Again, the design earthquakeis a magnitude 6.5 event direct­ly at the dam site. The com­plicatingfeature ofthat dam isthatthererismuchdebateabout the possibility ofafaultgoing through the foundationof the dam and, therefore,directly through the dam.

The ConsultantBoardonwhich I served determined thatthe damought to be designedfor a fau Itoffset in .the fou nda­tion of about 6inches. Thatrecommendationledtoredesign ofthedamfromthethin archdamtoa concrete>"··gravity;aam...

The Uribante-Caparo project inVenezuela involves four damsand three powerhouses andsome parts ofthis project arebuilt about 15 miles from theBoconofault,which.isone ofthe largest faults in the world.

The seismic design of the pro­ject inVenezuela is an impor­tant controlling aspect oftheproject. The materialsavailable for building the damsthere are not the best in theworld. There is a lot of friablesandstone (friable meansbreak~El~~ily, from solid tosand), and so it turns out thatdesigning the dam to beseismically stable is a criticalaspect of the design...One ofth~dElsignearthq~akesisamagnitude7.5 event occurringabout seven miles from thedam;Thisisalmost identicalwith one of the possibledesign earthquakes fortheWatana dam unlessAcresissuccessf~LinprovingthattheTalkeetna thrust is notactive...

TheTalkeetna thrust is aJaultnear theWatanadam sitewhose activity is questionable,but it is believed to be inactive.If itremains in theinactivecategory, then the~everity ofshaking forWatanawillbeless than that for Uribante­Caparo projectingeneral.

The Pueblo ViejOproject inGuatemala is designed foramagnitude 7.75 earthquakepassing directly through theproject site-not the site ofthe dam,buttheoverallpro­jectsite. The fault passesthrough a power tunnel verycloseto the damsite. Theshaking there is of the order of0.7g acceleration, lasting formaybe 45 seconds---oneof themost severe seismic en-

vironments of any dam in theworld. Nevertheless, a safedesign has been worked outfor that project.

Incidentally, on all thesedams, designs have been pro­duced which have been ade­quate to accommodate themotions produced by theearthquakes. It is a matter ofhow you build the dam, howyou arrange the dam, whatmaterials you use in the dam,and how you place thematerials in the dam. Thesefactors will determine whetherthe dam will adequately with­stand the effects of the earth­quake.

" ...on all these dams,designs have been pro­duced which havebeen adequate to ac­commodate the mo·tions produced by theearthquakes. It is amatter of how youbuild the dam, how youarrange the dam, whatmaterials you use inthe dam, and how youplace the materials inthe dam."

QUESTION: What knotty pro­blems have you encounteredon other hydroelectricprojects?

SEED: AnY.problElmsthatyouencountElrare.El~sElntiallyrelCitedtothree major. .ones--- the amount of water tobe stored and the amountofflooding water that has tObestored at any given time; thestabiIity.of the foundationmaterials; and thepossible.ef­fectsof fault~in.trefpunda- .tio~. The firstis not my area ofexpertise. It isahydrologicalproblema~dthereareother

specialists who can ha~dle

thatpart of the problem. Iwould say the. most difficultpro~lems,intheearthquakesense,areprimCirily those ofevaluatingthestability of thefoundation materials on whichdams aretobe built.

For example, there was muchdebate about the safety duringearthquakes of RevelstokeDam in Canada and what theyshould do about the founda­tion. I was invited to be a con­sultant on that projectbecause of the different points

the susitna hydro studies/september 1981 5

The design of the Oroville dam in California, has been suggested as an appropriate model forpreliminary design of the Watana dam. It is an earthfill dam like Watana is proposed to be, is in aseismic area, and is of a similar height (Oroville is 770 feet, Watana is proposed to be 880 feet).

The design earthquake for Oroville was a magnitude 6.5 earthquake occurring directly under thedam site. The Oroville dam design can accommodate strong ground motions very near the damfor a relatively large earthquake.

of view aboutthe safety of thedam...

They were dealing with a verydifficult foundation soil. As amatter of fact, I told them thatthe foundation soils in someparts of the dam foundationbore a great resemblance tothose at Turnagain Heights inAlaska (the soils that failed inthe 1964 earthquake). Some ofthe foundation material forRevelstoke Dam reminded mealot of Bootlegger Cove clay. Itold them that it was anunstable materiCiI, especiallyat the level of shaking theywere designing for. I advisedthem,to excavate the materialout, and that's what theyelected to do. I would say thatwas a knotty problem.

Other knotty problems involvefaults in the foundation. Afterthe San Fernando dam nearlyfailed in the San Fernandoearthquake in California, thepeople living downstreamdidnot want another dam to bebuilt at that site, but it turnsout tobe acritical point.qfeno:;trance for water into California:for the cityofLosAngeles.Therefore, the DepartlTlent ofWater and Power in LosAngeles considered it essen­tial to have a reservoir in thata~ea, and. it was necessary torebuild the dam at that loca­tion. There was a possibility ofaJault movementinthefoun­dation, sowe hadto devise aspecialdesign which couldac­commodate a very high level ofshaking and the possibility ofafault movement in the foun­dation both occurring at thesame time. That was suc­cessfully done.

" ...itis a comfortingfactthat tit the p~esent

level ofknowledge oftheSusitna project,the. intensityofsha.k·ing whichcanbean·ticipated at eitherdamsite is considerablyless than those areasfor whichwe havealrea(jy de~igneddams."

The Teton dam involved pro­blems with highly erodiblesoils. The dam failed, but Ibelieve that if the design hadbeen modified, a safe damcould have been built at thatsite. The knotty problem there

was assessing the effect ofthe jointing of the rock and thesimultaneous erodibility of thesoils used to build the dam onthe safety of the dam. Thatwas a tricky problem. Theengineers whomade thedesign thought they had solv­ed it, but as events eventuallyproved, they had not. The damfailed. I believe we knowenough about it nowthat wecould rebuild the dam verysafely...To tell you the truth, I don'tknow of any dam whichdoesn't involve one or twoknotty problems.

QUESTION: How d()13stheseismicity of the Susitna areacompare to the seismisity ofotherregionswhereyotl?tlaveworked?

SEED: I would say that theseismicity of the Susitna arE)aas it .is pres13ntly un~13rstood

(and if it is established) issomewhat less than tl:1atwhich I have encountered inother parts of theworld. Thereare a number of faults whoseactivityhasnqt yett>eeQestablishedJntheSu~itna

area.TheYCi~ElbelieY13dto·beinactive faults,butttley areonrecord for being investigatedvery carefully during the. 1981summer.TheJalkeetnattlrustfault is one oftheseandpro~

bably ttle.mos~JITIP()r1Clptof

them..Ifall.th13JCiUI.tsthCltiarepresentlynotc lea~ly recog niz­ed as active are found to be in­active,t11enthe seisrnic:i~Yof

the Susitnaar13a (orth13:intE)n­sity qfgroundshakingthatwould develop) would not beas strong as many of the. damsthatwehave already designed.

QUESTION:And what if the op­posite were true?

ANSWER: If the.opposite weretrue,ifthe Talkeetna trustturns out to be an active fault,then the level of shaking atSusitna would be comparableto that ofsome ofthestrongest seismicregionswhere dams have been built.

Since we have beenable tobuild and design dams whichcan be shown tobe seismical­ly stable in those regions, thenI believe that the same techni­ques would be capable ofdemonstrating the same thingfor the dams of the Susitnaproject.

The design in any case will re­quire great care, but it wouldrequire even more care if thosefaults like the Talkeetna thrustturn out to be active faults...

TherenCls beeQtremendqusprogressinit h13f.iElI~Rf. eCirth­qUClk13.engin1313ripg;and.theeaghqHG\~13o:;resi~tantdesign ofdalTlshas.been totally revolu­tionized in the last 10 years. Itis almost like thedevelopments of spacetechnology. Things we can donow,.ourunderstandingof theproblems now, are. sovery.much greaterthan theywere10 years agothatwecanJeelenormous confidence now incomparison. In those dayspeople felt confident becausethey didn't really understandthe problems. Now we feelconfident because we have avery goodunde~standingof

the problems.

QUESTION: Can you givesome examples of why youcan be so confident?

SEED: We can point to virtuallydozens of dams which havewithstood very strong earth­quake shaking, even thestrongest imaginable earth­quake shaking. In California, in1906 there were at least 15dams within 5 miles of the SanAndreas fault on which amagnitude 8.3 earthquake oc­curred, and they were built bythe rather primitive pre-1900

construction methods. Tnerewasn'ta singleone of themthat sufferedany majordamage due tothe earthquake.During the last 10 years wehave learned whatthep[oper­ties of those dams are thatenabled them to.do that. Wecan also pointtoafew damsthat have failedduringearth­quakes andwtlatwe havelearned oyer the last10 yearsis what made those dams failas compared with the otherones that haven't failed.

" ...the earthquake·rf:tsistant design ofdams has been totallyrevolutionized in thelast 10 years."

The record is very positive.There have been literally hun­dreds of dams which havewithstood strong earthquakemotions. In the total history ofthe United States, so far as Iknow, I think there are onlyfour or five known failures ofdams during earthquakes, andsome of those were quitesmall dams...We better

understand which ones arelikely to be vulnerable andwhich ones are likely to besafe and how to transform theunsafe ones into safe ones...

In the most recent survey ofthe safety of dams in Califor­nia, the conclusion was thatthere are no dams in Californiawhich are a threat to thepublic... ln the last 10 yearsthere have been a number ofdams in California which havebeen recognized as earth­quake hazards that have eitherbeen taken out of service orrebuilt or modified in someway to eliminate the threat tothe public.

California is obviously one ofthe more seismically activestates in the United States,along with Alaska, and if wecan do it here, you can do it inAlaska, too.

6 thesusitnahydro studies/septemberi1981

Earth damscombine naturalmaterials andcarefulconstruction

Earth/rockfill dam:

"Any dam constructed ofexcavated materials placedwithout addition of bindingmaterials other than thoseinherent in the naturalmaterial. The materials areusually obtained at or nearthe dam site. "

-The InternationalCommission onLarge Dams

Earthlrockfill dams containabout 25 percent earth to re­tain the water and 75 percentrock to hold the earth up andensure stability.

In seismically active regions itis not unusual to flatten theslopes of the dam more than innon-seismic areas. The actualslope and proportions at,a par­ticular site is dependent on thematerials available for con­struction and the size of thedesign earthquake.

One of the most important re­quirements for earth dams isthat the materials be selectedand compacted-and the foun­dation stabilized-so that set­tlement of the earth and rockis minimized. For dams in highseismic regions, any river bedmaterials under the dam whichwould be unstable duringearthquakes is either removedorimproved.The core

Theqor~.isamel11brane builtwithin an earth dam to form an

impermeable barrier. It may beof natural materials.(clays,sands,etc.)or preparedmaterials (cement or asphalticconcrete), or of metal, plastic,or rubber.

In the case of Watana, the coreis proposed to be of glacial till(a mixture of gravels, sands,silts, and clays). It would bemore than 400 feet thick at theriverbed level, and tapered toabout 30 feet in thickness atthe crest of the dam.

Unlike concrete, earth corescannot support their ownweight even though they are aseffective as concrete at im­pounding water. Gently slop­ing man-made mountains ofcompacted sand, gravel, androckfill are needed to supportthe dam's core and keep it inposition.

Location of core

In general, a centr~lly locatedcore provides the best securityunder earthquake conditions.A central core is illustrated inthe diagram of the Watanacross-section.

Design

Each earthlrockfill dam is uni­que - it§ Viatertightness andstablilityare.2ir~ctIYrel~t~d tothe materials.u§~2forits con­struction and the materialsupon which it is founded.

Earth/rockfi.ll.dams are usuallyconstructed in zones.The

primary purpose of this is toensure safety in terms ofstrength, control of seepage,and protection against crack­ing.

Earthquake-resistant featuresin earthlrockfill dams:

Some of these provisions arebeing considered for theWatanadam.

All earth/rockfill dams arecompacted to make them .dense.I n earthquake areas theprocess ofcompaction is nodiff.erentbut more compactionis done because denser rockprovidesm()re§tability.Mostm~terialscan·becorppactedby3to~pas§es.wit~he~vymachinery.Test§.{~rem~de.in

the field asth~darni§.I:>~il1gconstructed to ensure thatmaximum cC>r1'lpactioni§achieved.

All dams alsoha'le freeboard.This is the heightabo'le nor­mal water level and itallowsfor waves, floods,and ice_Inearthquake areas, additionalheight is added to allow forsettlement.

If there is a potential for wavespassing over the crestofearthlrockfilldams, the crestcan be treated so thatthewaves pass safely; Such awave could result fromaseismic disturbance ora land­slide into the reservoir_Preliminary studies indicatethere is no potential for land-

slides in the Watana reservoirbecau§eofthetopographiccharacter of the valley.

Earthlrockfill dams are. usuallyzoned for strength and stability.In earthquake areas, widerfilterzones are provided to in­crease stability.

111 addition, th~ materials inthefilterzones are selected topr()"id~self-healingof cracks.Thi§conservative approach in­creases the level of confidenceinthe design. The dam isdesigned not to crack anda.lsodesigned to self-heal ifitdidcrack.

SlopeProtection

l3othJ~cesofan earth da.111mustb~protected againststructural damage.

Thegownstrea.rnface needsprotection.ag~iqst naturalerosionangmaybe coveredwith grassed soil or rock.

The upstream face must beprotected against damageby wave action, ice, orfloating.debris.Variousmethods include rock (rip­rap), precast concreteforms, soil cement, orthewaterproofing membrane ofthe dam.

Source:The Engineering of Large Dams Part II, Henry

H, Thomas, 1976, John Wiley & SonsPublishers, New York, A Wiley·lnlersciencePublication.

Cross·~~f!!,~'1view _ ~ • Im"",o,,,om IIJ Co,m,W",

0-tpr~~p,:!ill1_e,p,Watana __~ \:W8;~;;\! IiiiiI 5<ml-,,"'o", '0"' m Rock O-,m""'"""earth dam ....:'.'i!).::;:: .;;;:::;~$' . t ···:c.:C?~:fiP.·:~-::.. !'P:-;:J\ Fine filter ~ Slope protection

Comparative view of Anchorage skyline

the susitna hydro studies/september 1981 7

Background information on proposed,Susltnaproject

IIIIIIIII•", ...\

'\ ,...- \ \\

The Susitna hydroelectric pro­jectas .clJrrently prPppseclin­volves two dams and reser- .voirs on the SusitnaRiver inthe Talkeetna Mountains ofsouthcentralAlaska.

The.project area is about 50miles.northeast of Talkeetna,Alaska and 118 miles north­northeast of Anchorage,Alaska.

The upstream dam, Watana,is

proposed to be developedfirst. It is currently being con­sidered as an earth/rockfilldam, approximately 880 feethigh. This would make it thefifth highest dam in the worldand the highest in NorthAmerica. It would impound a54-mile-long reservoir.

The downstream dam at DevilCanyon is currently being con­sidered as a concrete archdam approximately 635 feet

high. It would impound a28-mile long reservoir.

These dimensions'are approx­imate and subject to changeduring detailed design.

The feasibility study is beingmanaged and conducted byAcres American, Inc. for theAlaska Power Authority. Thestudies conducted to daterepresent the fi rst year of aplanned two-year study (1980

and 1981). A draft feasibilityreport detailing researchef­forts in 10 different areas in­cluding economics, engineer­ing, and environmentalaspects of the proposed powerproject is due in March nextyear.

How proposed Heightabovelowest Rated Rated Year of

Susitna projects Year River State founda· Crest Reservoir capacity capacity initialcom- or Nearest or Dam tion length capacity now planned opera·

Name pleted. Basin city Province Country type m m m3 x 10° (MW) (MW) , tion

compare with 'Bonneville 1943 Columbia Portland Oregon·Washington USA concrete 32 277 588 1,076 1938gravity

existing dams 'Glen Canyon 1964 Colorado Page Arizona USA concrete 216 475 33,305 1,021 1,431 1964arch

'Grand Coulee 1942 Columbia Coulee City Washington USA concre.te 168 1,272 11,795 7,460 10,830 1942gravity

"Hoover 1936 Colorado Boulder City Nevada·Arizona USA concrete 221 379 36,703 1,345 1,345 1936arch/gravity

DMica 1973 Columbia Revelstoke British Columbia Canada earth/ 245 792 24,670 1,736 2,610 1976rockfill

·Oroville 1968 Feather Oroville California USA earth 235 2,316 4,299 679 679 1967

'Devil Canyon (Proposed) Susitna Talkeetna Alaska USA concrete 200 378 1,235 0 400 (Proposed)( 2000 ) arch ( 2000 )

·Watana (Proposed) Susitna Talkeetna Alaska USA earth/ 271 1,662 12,347 0 800 (Proposed)( 1993 ) rockfill ( 1993 )

Sources: 'Corps of Engineers; Portland. Oregon ") "Major Dams of the World," T.W. Mormel, Interns'tional Waler Power "Civil Design, Stale of California. Oroville. CaliforniaaWestern Area Power Office, Golden, Colorado. ")and Dam Constructlon, Special Issue May 1981, Published by fPC 'Acres American, Inc.• Anchorage. Alaska 1 Meter = 3.25 Feet

S) Electrical.Electronlc Press Ltd.• Quadrant House. The Quadrant, -Acres American, Inc.• Anchorage, AlaskaSutton. Surrey SM25AS. England

Construction timed to match power demand

2010

..

existing and committed

Siago 3 - Drill Canyon400MW

Stago 2 - Walana 400 MW

2000

--

Stage 1 - Watana 400 MW

1993 19951990

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ZipITIII]

1980

3) the Devil Canyon dam with its 400 MW is completed in theyear 2000.

2) the additional 400 MW ofcapacity at Watana is ready foroperation in 1995; and

1) TheWatana dam,with 400 MW would be completed in 1993,which is the earliest possible date because of time periodsinvolved in project evaluation, permitting, and construction;

Possible staging 01' Susitna project

This diagram shows how the Susitna development would bestaged under the medium forecast of future energy reoquirements.Withthis energy demand and ensuring that ade·quate generating reserves are maintained, power costs would beminimized if:

StateD]

ready to buy it. The energyconsumption forecasts pro­vide estimates ofhow muchpower can be sold in the yearsahead.

The Power Authority's ap­proach, then, is to postponespending money for the nextstage aslongas possible toensurethat there is the.de­rne:ndfpcpurche:sil'lgthe pro­je9t1spolAtE:lr..Mpneyspent on aprojectllYtlose.powercannotbe sold is money wasted.

Waiting too long to constructthe next stage, howE:lyer,.islJ nacceptable becausE:ltherewould be an increasinglikelihood of not beingable,tomeet the peak demands. Ifthisoccurred,customerswouldhave togow... i.thO~.te.IE:lC!ricityduring.hi9tl.LJ~e. er.i8d~.Thus,abalancehasto est~uck.be,

tW,eeDPostponingCidclitional.iny~stm~ntsCind •.~l'lsuring.ade­quategenerationto meet peakloads.

NameMailingAddress

Cityl.-.I-..L--l-L-~-I...-.l-..J...-l.-..J

3) the Devil Canyon dam withan installed capacity ofabout 400 MW.

2) an addition to the Watanacapacity of another 400MW;and

1) the Watana dam with in­stalled capacity of 400MW;

Both the Watana caPe:sity e:d,dition and the peYil.8e:nY8Dproject couldbebroughtpnline earlier or atthe same time,if needed, while all threestages could be postponed ifdemand turned out to be lessthan anticipated.

The proposed Susitna develop­ment is presently envil%i.onedas having three distinctstages:

This staging providE:lss.orneflexibility in the seqLJE:lDs.eancltiming of construction:Atthesame time, there are certainconstraints on thatflexibility.

Meanwhile,the balancing hasIn stagingthe.Susitnadevelop- to be done in thel midst of. ament, the primary objective is great deal of unqertainty aboutto keep the cost of poweras what the actual demand forlo""as.possible.Thisisidone power is going to be in theby minimizing E:l~p.el'lcl..itures future. As time goesonandwhile selling as much of the future power demandsavailable power as possible, become more certain, the plan-But the power cannot be sold ned staging would be adjustedif there aren't consumers to suit actual conditions.

III

... --- .......... --_........I This public information document on the Susitna hydropower project wa~developed by the Alaska Power Authority

Public Participation Office, Nancy Blunck, Director: Comments on the substance of this newsletter and ideas forfuture publications should be forwarded to the Public Participation Office by way of the following coupon.

Last First Initialiii iii iii I Iii iii I Iii I

If you wantto get futurenewsletters

Independent panel reviewingSusitna feasibility studies

8 the susitna hydro studies/september 1981

Dam at Devil Canyonrecommended over tunnel

Six leading scientists and government work on American Following 2,500 manhours of severely depleted because theengineers have been named to dams, he has extensive con- study (in excess of one man water would be flowingan independent external suiting experience with Cana- year of effort) a twin power tun- through the tunnel instead.review panel by the Alaska dian hydroelectric projects. nel plan has been eliminatedPower Authority Board of as an alternative to a dam at The kayaking experience atDirectors. The specialists, who Dr. A. Starker Leopold is a Devil Canyon. Devil Canyon could be pre-collectively have more than distinguished zoologist who served, but not in the same200 years' experience in their has been associated with the The tunnels, 15 miles long and way that it exists now. With afields, are reviewing the Susit- University of California since 30 feet in diameter, were tunnel, kayaking would bena feasibility studies con- 1946. A one-time vice- eliminated from further con- dependent upon the controlledducted by Acres American and president of the Sierra Club, sideration when it became release of water through theother research contractors. hehas served on many wildlife clear that they would generate canyon.

and conservation organiza- 26% less electricity and wouldInterview with members of the tions and has conducted ex- cost $637 million more than a In addition, by virtue of sizereview panel will be available tensive research around the dam at Devil Canyon. alone, construction of thein future publications as the world. smaller re-regulation dam (245specialists comment on The difference in energy out- feet) would have less en-general plans for the Susitna Dr. Andrew H. Merritt is a put, primarily due to friction vironmental impact than thedevelopment and specific geologist who has been involv- losses along the length of the Devi I Canyon dam. The riverfeasibility studies. ed in the research, design, and tunnel, is equivalent to about miles flooded and the reservoir

review of major construction 30% of the total energy area created by the re-Exerpts from an interview with projecs around the world. A generated in 1980 by both An- regulation dam for the tunnelDr. Seed appear in this specialist in tunnels and rock chorage utilities (Municipal would be about half those ofnewsletter. work, he has extensive ex- Light and Power and Chugach the Devil Canyon dam, thereby

perience with hydroelectric Electric Association). reducing negative conse-Merlin D. Copen is an expert and nuclear power projects. quences such as loss ofon concrete dams. He has had In the long term, an additional wildlife habitat and possiblemajor responsibility for the Dr. H. Bolton Seed is a former generating plant would have to archeological sites in thedesign of the Glenn Canyon chairman of the Department of be added to fill this gap and reservoir area.Dam on the Colorado River, Civil Engineering at the this could create an additionalCalifornia'sAuburn Dam (pro- Berkeley campus of the source of environmental im- With the tunnel, there couldposed as one of the longest University of California. A pact which has not been in- conceivably be a rare mitiga-concrete arch dams in the specialist in earthquake eluded in thecomparison at tion opportunity of creatingworld), and many others. He engineering problems, he has this time. new salmon spawning habitathas consulted on numerous in- consulted on dozens of the in an 11-mile section of theternational projects as well as world's largest dam projects. Excluding consideration of river above Devil Canyon.other Alaskan developments. this additional generation to Presently, Devil Canyon

Dr. Dennis M. Rohan is an make up the shortfall, the tun- presents a physical barrier toJacob H. Douma served as economist with the Stanford nels' main advantages were fish migration.chief of the Hydraulic Design Research Institute who environmental. The adverse ef-Branch of the U.S. Army Corps specializes in energy matters. fects upon the aesthetic value Source:

of Engineers prior to his retire- He has been involved in and uniqueness of Devil Can- "Susitna Hydroelectric Project, Tunnel Alter-natives Report, Task 6, Design Development,"

ment from active government economic analyses of all yon would be lessened with a prepared by Acres American, Inc. for the

service after more than 40 phases of energy production tunnel, although the flows Alaska Power Authority, July 1980.

years. In addition to his and consumption. through the canyon would be

Douma

Merritt

Rohan

External ReviewPanel Members:

Leopold

Seed

Copen