IAN REPORT 171 - · PDF fileModeling of the Cougar Creek Debris Flood Retention Structure;...

University of Natural Resources and LifeSciencesDepartmentofCivilEngineeringandNaturalHazards

InstituteofMountainRiskEngineeringPeterJordanStr.82 Tel.:+43‐1‐47654‐4350A‐1190WIEN Fax:+43‐1‐47654‐4390

IANREPORT171

PhysicalModelingoftheCougarCreekDebrisFloodRetentionStructure

Vienna,February2016

2

Projektleitung: Univ.Prof.Dipl.‐Ing.Dr.HüblJohannes

Mitarbeiter: FalkensteinerMartin

Dipl.‐Ing.Dr.ChiariMichael

IliadisMarie

Reference: HÜBL, J., FALKENSTEINER, M., CHIARI, M., ILIADIS, M. (2016): Physical ModelingoftheCougarCreekDebrisFloodRetentionStructure;IANReport 171, Department of Civil Engineering and Natural Hazards, University of NaturalResourcesandLifeSciences–Vienna(unpublished)

Vienna,February2016

UniversityofNaturalResourcesandLifeSciences

DepartmentofCivilEngineeringandNaturalHazards

InstituteofMountainRiskEngineering

PeterJordanStr.82 Tel.:+43‐1‐47654‐4350

A‐1190WIEN Fax:+43‐1‐47654‐4390

IANReport171:

PhysicalModelingofthe

CougarCreekDebrisFloodRetentionStructure

3

Contents

INTRODUCTION ...................................................................................................................... 6

1 MODEL SETUP ................................................................................................................ 7

1.1 Froude scaling .............................................................................................................. 7

1.2 Construction of the model ............................................................................................. 8

1.2.1 Water supply ........................................................................................................ 8

1.2.2 Central model ...................................................................................................... 9

1.2.3 Stilling basin and erosion area .......................................................................... 16

1.3 Sensors and measurements ....................................................................................... 18

1.3.1 Discharge .......................................................................................................... 18

1.3.2 Water level heights ............................................................................................ 18

1.3.3 Thomson Weir ................................................................................................... 19

1.3.4 Height of throttle opening .................................................................................. 20

1.3.5 Volume of the bedload deposition an remobilization ......................................... 20

1.3.6 Bedload transport capacity in the culvert ........................................................... 21

1.3.7 Density of the bedload deposit .......................................................................... 21

1.3.8 Flow velocities ................................................................................................... 21

1.4 Rakes .......................................................................................................................... 22

1.4.1 Rake#1 .............................................................................................................. 23

1.4.2 Rake#2 .............................................................................................................. 24

1.4.3 Rake#2a ............................................................................................................ 26

1.4.4 Rake#3 .............................................................................................................. 27

1.4.5 Rake#4 .............................................................................................................. 29

2 EXPERIMENTS ............................................................................................................... 31

2.1 Hydraulic experiments ................................................................................................ 31

2.1.1 Types of the hydraulic experiments ................................................................... 31

4

2.1.2 Design of the outlet channel .............................................................................. 33

2.1.3 Effect of throttle design ...................................................................................... 36

2.1.4 Effect of rake designs ........................................................................................ 37

2.1.5 Effect of the inlet design and positioning of the rake ......................................... 39

2.1.6 Length of the overfall ......................................................................................... 40

2.1.7 Discharges at different storage levels ............................................................... 41

2.2 Experiments with woody debris .................................................................................. 42

2.2.1 Test setup .......................................................................................................... 42

2.2.2 Effect of rake designs ........................................................................................ 45

2.3 Experiments with bedload transport ........................................................................... 45

2.3.1 Setup ................................................................................................................. 45

2.3.2 Experiments ....................................................................................................... 47

2.4 Overflow scenario ....................................................................................................... 55

2.4.1 Velocity distribution ............................................................................................ 55

2.4.2 Stilling basin ...................................................................................................... 56

2.5 Investigations on the diversion tunnel ......................................................................... 60

2.5.1 Setup ................................................................................................................. 60

2.5.2 Hydraulic investigation ....................................................................................... 62

2.5.3 Sediment transport investigation ....................................................................... 67

3 CONCLUSIONS AND RECOMMENDATIONS ............................................................... 68

3.1 Hydraulic experiments ................................................................................................ 68

3.2 Experiments with woody debris .................................................................................. 68

3.3 Experiments with bedload transport ........................................................................... 69

3.3.1 Deposition behavior and remobilization of material ........................................... 69

3.3.2 Bedload transport in the outlet channel ............................................................. 69

3.3.3 Bedload deposition/erosion behavior in the ‘stilling basin ................................. 69

3.4 Overflow ...................................................................................................................... 69

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3.5 Diversion tunnel option ............................................................................................... 70

3.6 Scaling issues in hydraulic modelling ......................................................................... 70

4 REFERENCES ................................................................................................................ 71

5 ATTACHMENTS ............................................................................................................. 71

6

Introduction

CougarCreek ispartof theMountainCreekHazardMitigationProgram.After thedebris‐flood

eventinJune2013,establishinglong‐termmitigationbecameapriorityfortheTownofCanmore

inordertoavoidanothercatastrophicsituation.Indeed,thislastmountainhazardcausedsevere

damagesintheCougarCreekcatchmentandonthealluvialfan.Moreover,apartoftheTrans‐

CanadianHighwayandCanadian‐PacificRailwaywasdestroyed,breakingconnectionsbetween

Banff(WestofCanmore)andCalgary(BGCENGINEERINGLtd.,2014).Theshort‐termmitigation

was initiated early 2014 and completed in May 2014, one year after the devastating event

(CANMORE, 2015a), including excavations of the creek channel, cleaning out debris aggraded

duringthedebris‐floodof2013,constructionofchannelbedprotectionandadebrisnet,etc.

ManyscientificstudieswereconductedonCougarCreek,mainlyaboutgeomorphology,hydro‐

climate and watershed. For long‐term mitigation a debris flood retention structure was

recommended following an option analysis and evaluation phase. ALPINFRA CONSULTING +

ENGINEERINGGMBHandCanadianHydrotechCorp.arethemainconsultantsontheproject.

To support the process of planning, hydraulic experiments on a physical scale model were

performedattheInstituteofMountainRiskEngineeringofUniversityofNaturalResourcesand

LifeSciencesinVienna.

Scopeoftheprojectwas:

hydraulicoptimizationoftheoutletchannelgeometry.

optimizationsofroughnessintheoutletchannel;

investigationsontheeffectofdifferentthrottledesigns;

optimizationofthegravelrakeshape;

investigationsonsedimentdepositionintheculvert;

observationsofthelocationofahydraulicjumpand

investigationsondepositionanderosionofsedimentup‐anddownstreamofthedebris

floodretentionstructure.

7

1 Model Setup

1.1 Froude scaling

Inordertotransferalltheprocessesandconclusionsbetweenthemodelandreality,mechanical

similarity, which comprises geometric, kinematic, and dynamic similarity, has to be fulfilled

(Preissleretal.1989).Inopenchannelflows,theflowingmediumiswater,whichhasaverylow

Newtonianviscosity.Forphenomenawheregravityandinertialforcesaredominantandeffects

ofremainingforcessuchaskinematicviscosityaresmall,Froudescaledmodelsarepreferred.In

ordertokeepunavoidableerrorssmall,thegeometricalscalingfactorshouldbekeptassmallas

possible(i.e.thephysicalmodelshouldbeaslargeaspossible).ThescalefortheCougarCreek

modelwaschosentoequal1:30.

Incontinuummechanics,theFroudenumber(Fr)isadimensionlessnumberdefinedastheratio

oftheflowinertiatotheexternalfield.NamedafterWilliamFroude,theFroudenumberisbased

onthespeed–lengthratioasdefined:

∗

where v0 is a characteristic flow velocity, g is the acceleration due to gravity, and h is a

characteristic length (PREIßLERandBOLLRICH,1985). Equality in Fr in model and full scale

will ensure that gravity forces are correctly scaled.

InTable1thescalingratioalongfordifferentphysicalunitsisgivenbyλ,whichisthescaling

factorforFroudesimilarity.

Table1:ScalingratioalongFroudesimilaritylaw.

description symbol scalefunction(Fr)

length l λ

acceleration b λ0

pressure p λ

speed v λ1/2

discharge q λ5/2

time t λ1/2

8

1.2 Construction of the model

Fortheexperiments in the laboratoryof the InstituteofMountainRiskEngineeringaFroude‐

scaledmodelwithaphysicalscaleof1/30wasbuilt.

Duetoalimitedwidthofthelaboratorya30mwidesectionoftheretentionstructurewiththe

bottomoutletchannelinthecenterwasrepresentedbythemodel.Thelengthoftheupstream

channelbedwaslimitedto115minnaturaldimensions.Fortheupstreamchannelbedanaverage

inclination(3.5%)ofthelast165mupstreamwasused.Thegeometricdesignofthedamwas

plannedaccordingtospecificationsprovidedbyalpinfra.Theinclinationatthefootprintofthe

retentionstructurewas4.37%.Theinclinationoftheupstreamembankmentdamalsofollowed

theinformationfromalpinfra,butneglectingtheaccessroad.Afterall,theinclinationfromthe

lowesttothehighestpointofthedamcrosssectionwasused(38.1%).Toprovideabetterinsight

intotheprocessofthetunneldischarge,thedownstreamsurfaceofthemodelwasnotinstalled

forthefirsttests.Itwasaddedeventuallyforthe‘overflow’(2.1.1.4)testsinthelaststageofthe

modeling.

TheoveralldimensionsoftheCougarCreektestsetupreachedalengthof14mandawidthof3m,

including:

Thewatersupplywithwaterreservoir,Thomsonweirandbypass(3.05mlength).

Thecentralmodelwithriverbedsectionanddamstructure(8.9mlength).

Thesectionforthestillingbasinanderosionarea(1.6mlength).

Thefilterbasin,partlyplacedbelowtheerosionarea(1.24mlength,0.48moverlapping).

Aconveyorbeltwasusedtoaddbedloadmaterial.

1.2.1 Water supply

The configuration of our laboratory includes a 27m3 sub level water basin (see Figure 7). A

circulatingpump (type:Grundfos ‐ CLM150‐271‐18.5A‐F‐A‐BBU)bringsup thewater (up to

50l/s)andfillstheso‐called‘ThomsonBasin’.

SubsequenttotheThomsonBasinisanintermediatebasinwithbypass,whichallowstosuddenly

stopthedischargeinthemodel(Figure1).

9

1.2.2 Central model

Themainmodelwasbasedon10reinforced‘U‐profiles’madeoutof10x10cmsquareshaped

timber.The‘U‐profiles’hadaninnerwidthof120cmandaheightof150cm(seeFigure9).

The profileswere placed in a linewith a distance of 100cm from each other and horizontal

leveled.Averticallyplacedrasterframeworkoutofathree‐layersheeting(company:doka)was

placed on the base structure, following the specified inclinations for the channel bed and the

embankment dam structure (see Figure 2). Sheeting boards (1m wide) were placed on that

framework,providingthebaselayerforthedamstructureandasealingfoil.

Further,1.5mwidethree‐layerboards,fixedverticallytotheleftandrightandtheupstreamhead

endofthemodel,flankedthebottomconstruction.Thesidewallsweresupportedbytheabove‐

mentionedu‐profiles inavertical, and20x8cmH‐beamtimber inahorizontaldirection.The

modelofthedamstructurewasplacedinthischannel,sotheretentionbasinwasformed.The

foundationwasthencoveredwithanimpermeablefoiloutofEPDM‐material.

Figure1:Watersupplyinstallations.

10

Additionalsheetingboardsforfurtherinstallationswereplacedonthesealinglayer.Anadditional

basinwithscumbaffle(breakingthevelocityoftheinflow)wasfixedontheboards,placedonthe

channelbedsection.Thechannelroughnesswasplacedonthoseboardstoo.Theboardsatthe

upstreamslopeoftheembankmentdamsupportedtheinstallationofthethrottle,thedifferent

inletdesignsandrakes.

1.2.2.1 Dam slopes

Theupstreamdamslope showeda rectangular, rake‐coveredbypass channel,with awidthof

33.3cmandadepthof8.33cm, including therakeconstruction. If the lowerrakestructure is

clogged,watercanpassthroughthisbypassandwilldischargethroughintotheoutletchannel

(seeFigure3).Thisensuresacontrolleddischargedownstreamthedam.

For the downstream face of the dam it was needed to install an adequate roughness,

correspondingtoriprapinnaturaldimensions(seeFigure4).Theinclinationof30°followsthe

requirementsofalpinfra.Thedesignofthetransitionreachbetweendamfootandstillingbasin

wasadaptedduringtheproject.

Figure2:Baseframeworkofthemodel(Iliadis,2015).

11

Figure3:Upstreamdamsurface,rakeandinletdesign. Figure4:Downstreamdamstructure.

12

1.2.2.2 Culvert

Theculvert channelwasdesignedasa sealedU‐profile,one sidewallmadeoutof transparent

acrylicplastic.Witha lengthof4.34m it reached fromthe throttle to theendof thedamand

followedtheinclinationofthedambase.Thisbasicstructureenabledtheinstallationofdifferent

culvertdesignsandfacilitatedobservationsthroughthetransparentoutlet(seeFigure10).

1.2.2.3 Inlet design

Arectangularcuttinginthedamstructure(horizontaldistanceof78cmfromtheintersectionof

theupstreamdamsurfaceandthechannelbed;widthof33.3cm)incorporatedtheculvertinlet

andthethrottlestructure.

Upstreamoftheinletahydraulicallyconvenientbottleneckwasshapedtominimizeenergylosses.

Along this narrowing the slope of the side walls was 4V:1H at the stone-pitched bottleneck

(height of 10 cm) and then transitions to the circular shaped outlet channel design. Thisdesign

wasconstructedbyshapinginsulationboardsandaddingriprap(accordingtothephysicalscale

ofthemodel)inthesectionupstreamoftherakestructure(seeFigure5).

1.2.2.4 Throttle

Thethrottlewasdesignedasverticaladjustableslide(27x24x1.2cm)infrontoftheculvertinlet

(seeFigure6).Theoverlappingdesignguaranteedasealedperformance.Ameasuringscalewith

verniersupportedthedetectionofaccurateadjustments.Fortestingdifferentthrottledesignsthe

throttlecouldbechangedeasily.

Figure5:Inletdesignandthrottle.

13

1.2.2.5 Water supply to the basin

Attheupstreamendoftheretentionbasinanadditionalbasinwithascumbafflewasinstalledin

ordertogethomogeneousinflowconditionsoverthewidthofthemodel(seeFigure7andFigure

48).

Figure6:Upstreamdamsurfacewithadjustablethrottle.

14

Figure7:Longitudinalsectionplotmodel(dimensionsincm).

15

Figure8:Planviewphysicalmodel(dimensionsincm).

Figure9:Sectionplotmodel(dimensionsincm).

16

1.2.3 Stilling basin and erosion area

Asimplesealedwoodenframeworkwithalengthof1.6mandawidthof1mformedthissection

asahorizontalbasin.Athree‐layerboardseparatedthebasinintwoparts,sothedimensionsof

the stillingbasin couldbeeasilymodified (seeFigure10).Theheightof the separationboard

followedthespecificationsofalpinfra;theheightoftheboardattheendofthemodelisbasedon

theinclinationoftheculvert.Duringtheperiodoftheoverflowinvestigation,theframeworkwas

adaptedtoassessthissectioninmoredetail.

Figure10:Stillingbasin,erosionarea andculvertstructure.

17

Figure11:Overview:physicalsclaemodelbasedesign.

Figure11showsthewholemodelincludingtheconveyorbeltintheback,thespillwaythestilling

basinanderosionarea.

18

1.3 Sensors and measurements

1.3.1 Discharge

Thepumpingcycleofourlaboratoryincludesaflowmeterbetweenthecirculationpumpandthe

Thomsonbasin.Thisflowmeter(SIEMENSSITRANSFMMAGFLOWMAG5000)informedabout

theactualdischargeinl/s,andwascontrolledbytheThomsonweir(see1.3.3).

1.3.2 Water level heights

Figure 12 shows an ultrasonic sensor ‘UC500‐

30GM‐IUR2‐V15’ (PEPPERL + FUCHS GROUP,

2014).

Six ultrasonic sensors of this type were used

duringthetests.SensorUS_1wasplacedinfront

of the rake, sensor US_5 directly upstream the

throttle. Both were set close to the ground and

whenwaterwasnotretained,fortestswithhigher

waterlevelsthesesensorswereremoved.Sensor

US_2 gave information about the water level at

filledupconditions.US_2wasinstalledontheleft

sidewhenwaterwasflowingandatthelevelofthe

left sidewall of the model (see Figure 13). Two

other sensors (US_3, US_4) were placed in the

tunnel, one at 2m and the other at 3,5m

downstreamthethrottle.

Figure13:Positionsoftheultrasonicsensors(dimensionsincm).

Figure12:UltrasonicsensorPEPPERL&FUCHS.

19

Thesensorsmeasurethedistancebetweenthebaseofthesensorandthewaterlevel(Figure14).

Knowingthedistancebetweenthefixedsensorandthegroundlevelofthemodel,thewaterlevel

canbedetermined.Theultrasonicsensorswereoperatedwith10Hz.Theresponseofultrasonic

sensors is linear with distance and independent upon the reflectivity of water (ROCKWELL

AUTOMATIONInc.,2015).

1.3.3 Thomson Weir

Thesixthsensor(US_Thomson)wasplacedabovetheThomsonbasin(seeFigure7).Theoutlet

of this steel tankhadaV‐shapedprofilewitha specifiedangle.Combinedwith theUS‐sensor,

whichshowedthewaterheight,theaccuratedischargewascalculatedtocontrolthesignalfrom

thepump(seeFigure15).

AccordingtoPREIßLERandBOLLRICH(1985),thisV‐shapehelps,tocalculatethedischarge:

815

∗ μ ∗ 2 ∗ ∗ /

With:μ 0.565 0.0087/√

Theparameters , , andμcorrespondto:

,thedischarge(m3/s)

,thegravitationalacceleration(m/s2)

,theheightofthewaterlevel(m)

μ,thedischargecoefficient

Figure14:Drawingofthemeasuredparameterwithanultrasonicsensor.

20

Figure15:DrawingoftheV‐shapedThomsonbasin(adapt.formPREIßLERandBOLLRICH,1985).

1.3.4 Height of throttle opening

Tomeasuretheopeningofthethrottleattheinletofthetunnel,avernierscalewasinstalled.One

sidewasfixedtothetopofthethrottleandthus,therulerwasmovingatthesametimeasthe

throttle(seeFigure16).Thethrottleopeningisdefinedastheheightbetweenthebottomofthe

outletchannelandthebottomedgeofthethrottle.

Figure16:Vernierscalemeasuringthethrottleopeningheightanddetailofvernierscale.

1.3.5 Volume of the bedload deposition an remobilization

Atwo‐stepprocessgeneratedthedataforbedloaddepositionvolumesintheretentionbasin.

1. In the first step the surface data was generated by using photogrammetry. For this

purpose the Agisoft PhotoScan softwarewas used. Eight targetswere attached to the

modelandreferencedtosetdimensionsinthelab(seeFigure48).Duringabedloadtest

runregularbreaksweredonetotakephotoseriesofthedepositedbedload.Thesoftware

21

automaticallydetects the targets, andgenerates a3D‐model.For thenextprocess the

modelwasexportedasTIFFfile.

2. The‘Surfer13’(GoldenSoftware)programwasusedtocomputethedepositionvolumes

of the3D‐models.Therefore itwaspossible to compare thevolumedataandvisualize

growthorre‐mobilizationofsediment.

1.3.6 Bedload transport capacity in the culvert

Sedimentwastransportedthroughtheculvertatdifferentstagesofthebedloadtests.Togetthe

informationaboutthetransportcapacity,sedimentwastrappedatthedownstreamendofthe

culvert.A0.5mm(DIN4188)sievewastakentofilterthematerialforaperiodof1minuteper

sample.Thesamplesweredriedandweighted,andanaveragevalueontheremoval‐timewas

calculatedtogettheunitkg/s.

1.3.7 Density of the bedload deposit

Fordensitymeasurementsofthesedimentasamplingring(innerdiameter:9.9mm)wasused.

Sedimentwassampledwith thesamplingringat3positions in theretentionbasin:1.2,2and

2.7mupstreamthethrottle(Position‘0’),inthemiddleofthebasin.Thesamplesweremeasured,

driedandweighed.

1.3.8 Flow velocities

Forrecordingthevelocitydistributionatthedownstream

faceofthedamandintheoutletchannelaflowmeterfrom

Schiltknecht(MC20)wasused.Thesmalldiameterofthe

impeller (1cm inner diameter) helped to measure at

smallflowheights(Figure17).Thechangedwatersurface

heightcausedbyentrappedairatthelowersectionofthe

dam, precluded flow velocity measurements based on

ultrasonicsensors.

Figure17:Flowmeter:SchiltknechtMC20.

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1.4 Rakes

A central question for the physicalmodelingwas to develop a rake structure thatmeets the

followingrequirements.

Therakeshouldnotaffecttheflowconditionsatthethrottleinadisadvantageousway.

Woodydebrisshouldbetrapped,toavoidblockingatthethrottleandtheoutletchannel.

Smallbedloadtransportingeventsshouldpassalmostundisturbedthroughtheculvert

buttherakeshouldfilterthecoarsestfractions.

Thetechnicalpracticabilityonrealisticconditionsshouldbegiven,andthefrontshould

bemodifiableforlateradaptions.

Thus, different rakes were in

discussionandtestedduringthe

experimentstomeetthevarious

issues. The designs of Rake#2

andRake#2awere provided by

alpinfra, Rake#1, Rake#3 and

Rak#4 were developed at the

Institute of Mountain Risk

Engineering.

With the exception of Rake#1

therakebeamsweremadeoutof

especially cropped 10to10mm

aluminumH‐profiles.Otherdetailsandmostoftherequiredintersectionswererealizedby3D‐

printedcomponents(seeFigure18).TheverticalbeamsofRake#1showedaroundcrosssection

withadiameterof10mm,butontheuppersideH‐profilebeamswereplaced.

Figure18:Model:Rake#4.

23

1.4.1 Rake#1

Likeabove‐mentioned,the

verticalbeamsof‘Rake#1’

were made with round

profiles. Also the

upstreamfrontoftherake

showed a half circular

section (see Figure 21)

with a radius of

176.65cm. The distance

betweenthesinglebeams

was 2cm. The upper

beams showed a distance

of1.5cm.Onbothsidesof

the rake additional

(concrete)‐flapssimplified therakestructureandguaranteedbeneficial flowconditionsat the

throttle(seeFigure19).Thehydraulicconvenientverticalbeamsandtheenlargedsurfaceofthe

crosssectionshouldenhancehighdischargeswithoutclogging.

Figure20:Longitudinalsection:Rake#1(dimensionsinmm).

Figure19:3D‐plot:Rake#1.

24

1.4.2 Rake#2

Rake#2wasdesignedasa

simple rake following the

inclination of the dam

structure. The front

section was built of

vertical H‐profile beams,

which end 3.42cm above

the bottom.Thatdistance

correlatedwith thewater

heightof8m³/sdischarge

at this position. The

distance between the

beams was set to 1.5cm

(see Figure 22 to Figure

24).

Figure21:Planview:Rake#1.


25



26

1.4.3 Rake#2a

The differences between

rake#2 and rake#2a

(Figure 25 to Figure 27)

were in length and

distance of the rake front

to the ground. Therefore

the rake was pushed

forward to the position

wherethelowerendofthe

rakemetadistancetothe

bottom structure of

1.5cm.

Figure26:Longitudinalsection:Rake#2a(dimensionsinmm).

Figure25:3D‐plot:Rake#2a.

27

1.4.4 Rake#3

Rake type#3 showed two

kinks, the upper one at a

height of 9,7cm over

ground, the lower one at

6cm (see Figure 28 to

Figure 30). The beams on

thefrontsideended1,5cm

above the ground. The

inclination of the flatter

middle section was 14°.

The distance between the

beamswasagainspecified

with1.5cm.Thattypewas

plannedtofilteroutwoodydebris.Thesmallheightofthefrontbeamsforcesthewoodydebris

todepositattheflat‐angledareaaboveandsoavoidclogginginthelowerparts.

Figure27:Planview:Rake#2a.


28



29

1.4.5 Rake#4

Rake#4 (Figure 31 to

Figure 33) included two

disks to support the rake

and avoid clogging by

woody debris.

Additionally, the disks

enhance water velocities

at the rake and increase

self‐cleaning effects after

sediment deposition. The

disks were designed as

triangleswitha45°angle,

andathicknessof1.67cm

(0.5mnaturescale).Theupstreamedgeswereconstructedwithroundprofiles;thelengthonthe

basewas11.67cm(3.5mnaturescale).



30

Figure33:Planview:Rake#4

31

2 Experiments

2.1 Hydraulic experiments

Thehydraulicexperimentsshouldansweraseriesofissuesaroundtheoutletchanneldesign,the

inletstructureandthrottleconstruction,aswellastherakestructure.Fourmaintestsetupsfor

thehydraulicexperimentsweredeterminedtodeliversufficientresults.

Thehydraulicexperimentswereoperatedwithsteadystateconditions.Thatmeans,atestneeded

toshowconstantvaluesoveralongerperiodoftime.Onlywhensteadyconditionsappeared,the

measuredvalueswereusedforevaluation.Fromtheacquiredvalues,ameanvaluewascalculated

whichcanbefoundintheresulttables.

2.1.1 Types of the hydraulic experiments

2.1.1.1 Full basin (FB) test:

Inafirststep,theparticularsetupwasrunwiththeso‐called‘fullbasin’or‘FB’test.

The retention basin was filled up with water to its top (see Figure 34). Then, the particular

dischargewassettothewatersupplypump.Now,thethrottlewasadjustedtotheaskedmaximal

flows,sothatthewaterheightintheretentionbasinstayedconstantoveraspecificperiodoftime.

Figure34:Retentionbasinat'fullbasin'conditions.

32

2.1.1.2 Maximum discharge (MD) test:

In a second step, themaximum free surface flowwithout backwater effect at the determined

throttleheightwastested.

Therefore the throttle

specifications from the ‘FB’ tests

were used and the discharge

graduallyincreasedfrom‘0’tothe

level where it showed the first

backwater effects at the throttle

(see Figure 35). This information

wasrequestedfromtheengineers,

because the retention of water

changes the flow conditions

upstreamthestructureandforthis

reasonsitalsoaffectsthebedload

transportsituation.

2.1.1.3 Normal flow (NF) test:

The‘NF‐tests’focusedondischargesbelowthe‘maximumdischarge’.Waterheightsonspecified

positionsupstreamtherakestructureweremeasured,upstreamthe throttleand in theoutlet

channel.Thatsetupprovidedinformationontheeffectsofdifferentraketypesandfortheannual

flows.

2.1.1.4 Overflow (OF) test:

Forapossibleoverflowevent,a318m³/sscenarioinnaturalscalewasrequested.The318m³/s

scenario(64.5l/sinthemodelscale)wouldleadtoanovertoppingoftheretentionstructure.As

ourmodelwas limited to awidth of 1m andour pump to 50l/s, itwasneeded to adapt the

experiments.According toaproposalofalpinfra,webuilt inanarrowing to75.4cm(22.6m)

widthatthedownstreamfaceofthedam.Operatedwithadischargeof48.7l/s(240m³/s)the

setupmatchesthesameheightoftheoverflowingwateratthedamcrest.The‘OF’‐experiments

investigatedtheflowvelocitiesalongthedownstreamfaceofthedam,theflowconditionsinthe

stillingbasin, thebedloadbehavior in the stillingbasinand theerosionarea. Someadditional

installations(chuteandbaffleblocks)were tested.Apart fromthevelocitymeasurements, the

effectsweredocumentedwithpicturesandvideos.

Figure35:Throttleatmaximumdischargeconditions.

33

2.1.1.5 Classification

ForabetterorientationaTest‐IDsystemtonumberthesingleexperimentswasused.Thecode

containsaseriesofnumbersandlettersdescribingthetestsetup.

2.1.2 Design of the outlet channel

Intheprogressofprojectplanning, thecrosssectionof theoutletchannelwasoneof the first

issuesthephysicalmodellingshoulddealwith.Theideawastoconstructanoutlettunnel,which

canbeusedforthedischargeaswellasfortransportofdepositedbedloadmaterialbytrucks.

Therefore theoutletchannelhad toprovidea tunnelwithappropriatedimensionsof5.5m to

5.5mforthetrucksandanadditionaladischargechannelbelow.

Therefore, a squared U‐profile basic structure with the maximum required dimension was

installed(Figure10).Lateron,thechannelprofilestotestwereinstalled.Athrottlewasfixedat

thechannelinlet,toreducethecrosssectionalareaaccordingtotherequireddischarge.Forthe

tests,thethrottlewasadjustableinitsheightbyathreadedrod,tofindtheadequateadjustment

bytesting(seeFigure6orFigure16).

Pos1: H‐(for‘hydraulics’)testwithonlywater;BL refersto‘Bedload’.

Pos2: E‐theoutletchannelhasarectangularprofile;Rincludesaroundprofile.

Pos3: OO‐fornorake;RaforRake#1;RbforRake#2;RcforRake#3;RdforRake#4;Refor

Rake#2a.

Pos4: 06,08,10,…,50,60or100forthevalueofthedischargetested(m³/s),

Pos5: FBforthesimulationtype‘fullbasin’;MDforthesimulationtype‘maximaldischarge’,

NFfor‘normalflow’tests.

Pos6: 001showsthesequencenumberofthetest.Ifatestwasrepeated,thenumberrose.

Examples:

The filenameHE0050FB_001means: it isahydraulic testwith therectangularprofile intheoutlet

channel,withoutrakeandthetypeofsimulationis‘fullbasin’.Itisalsothefirsttest.

HRRd06NF_002:hydraulictestwiththeroundoutletchannelprofile,rake#4wasinstalled,adischarge

of06m³/srespectively1.22l/swasused.Itwasa‘normalflow’testtypeandthesecondtestwiththis

setup.

34

2.1.2.1 Test with rectangular outlet

channel

Following the specifications of alpinfra, a

rectangular channel crosssection (seeFigure36)

wastestedwith45,50,60and100m³/s.Thegoal

was to find the particular throttle opening to

achieveamaximumdischargeof45m3/sunderfull

storagecondition.(‘fullbasin’:compare2.1.1.1)In

a second step the maximum free surface flow

without a backwater effect for each throttle

adjustment was tested. (‘maximum discharge’:

compare2.1.1.2)

InTable2theFroudeconversionfortherequireddischargesisshown.

Table2:Froude‐scalingthespecifieddischarges.

Q real (m³/s) Q model (l/s)

40 8.11

45 9.13

50 10.14

60 12.17

100 20.29

Afterrunningthe‘fullbasin’and‘maximumdischarge’experimentswiththerectangularoutlet

channel,theresultsgiveninTable3canbeshown.Figure37showsthecorrespondingthrottle

openingheights.

Table3:Resultsofhydraulicexperimentswithrectangularoutletchannel.

Rectangular outlet channel

Model condition Real conditions

Discharge Opening height: Throttle

Maximum discharge

DischargeOpening height: Throttle

Maximum discharge

l/s cm l/s m³/s m m³/s

9,13 3,83 2,80 45,00 1,15 13,80

10,14 4,48 3,30 50,00 1,45 16,27

12,17 5,49 3,90 60,00 1,65 19,23

20,29 6,89 7,00 100,00 2,07 34,51

Figure36:drawingoftheoutletchannelsection(dimensionsincm).

35

Throttleopeningheightfor29mpressureheadat

a) 45m3/s

b) 50m3/s

c) 60m3/s

d) 100m3/s

2.1.2.2 Tests with round design of the outlet channel

The Institute ofMountainRiskEngineering

suggestedaroundchanneldesignforbetter

sedimenttransportonlowerdischarges(see

Figure 38). The Town of Canmore reduced

the maximum discharge to 45m³/s. Thus,

‘full basin’ and ‘maximal discharge’

experiments were run with the specified

maximum discharge only. A roughness

correspondingtoasteelsurfacewaschosen

for these investigations to protect the

originaloutletchannelprofilefromabrasion

by bedload transport. Furthermore, the

smoothsurfacepreventssedimentdeposition.

Forthe‘fullbasin’testsawaterheadof29.85m

(inrealscale)at the loweredgeof thethrottlewasaskedbyalpinfra.Forthiswaterheadthe

experiment determined a throttle opening height of 4.34cm ‐ 1.3m in real dimensions. The

Figure37:Differentthrottleopeningheights(dimensionsincm).

Figure38:Roundchannelcrosssection(dimensionsincm)

36

‘maximum discharge’ test showed a discharge of 2.75l/s, which means 13.6m³/s for real

conditions.

Thefollowingexperimentswereallrunwiththerounddesignoftheoutletchannel.

2.1.3 Effect of throttle design

In anext step, effectsof different throttledesigns shouldbe shown.To this end, two typesof

throttleswere compared, inwhich themain designwas the same, but the lower edge shape

changed(seeFigure39).Thetest‐IDwiththeadditional‘a’inTable4,showstheexperimentswith

the45°angleshapedthrottle.

As it can be seen in Table 4, the throttle

openingheight varied0.5mmand led to a

differenceof3.4mmofthewaterheight in

the retention basin. Considering the

accuracy of the single measurements and

the period of several hours to get stable

conditions the presented deviations are

negligible. It has to be mentioned, that a

hydraulically optimized design would lead

toanoutletwithasmalleropeningheight.In

ordertomaximizethe‘maximumdischarge’

that does not result in backwater effects, a

hydraulic unfavorable design is preferable.

Thisisthereasonwhynootherdesignsliketaintergatesorrollinggatesweretested.

Table4:Effectsof2testedthrottledesigns.

US_2 Pump Throttle

opening height Square area

[mm] [l/s] [cm] [cm²]

HR0045MD_001 2,76 4,34 33,04

HR0045MDa_001 2,75 4,39 33,55

HR0045FB_001 969,29 9,14 4,34 33,04

HR0045FBa_001 965,88 9,14 4,39 33,55

Figure39:Comparedthrottledesigns(dimensionsincm).

37

2.1.4 Effect of rake designs

Themodelrunsshowedthatwithafilledbasinthedifferentraketypeshavenoeffectontheflow.

Thus,wefocusedontestsat‘normalflow’(compare:2.1.1.3)conditionstoobservetheinfluences

ofdifferentrakes.Thedischargewassetinstepsof2m³/sinnature,from6to14m³/s(see

Table5).

Table5:ConversionafterFroude:Naturetomodel.

Theheightoftheflowwasmeasuredat3Positions:

Upstreamoftherakestructure(pos:‐98).Dependingontheparticularrake,thedistance

betweenrakestructureandmeasurementchanges.

10cmupstreamthethrottle(pos:‐10).

Intheoutletchannel,200cmdownstreamthethrottle(pos:200).

This setup specified the hydraulic properties for the 5 tested rake types. Figure 40 shows a

comparisonofallraketypesatdifferentdischarges.

Nature Model

m³/s l/s

6,00 1,22

8,00 1,62

10,00 2,03

12,00 2,43

14,00 2,84

38

Figure40:Heightsoftheflowat3positionsalongthemodel.The‘0’‐Lineshowsthepositionofthethrottle.Position‘‐98’isjustupstreamtherakestructure,position‘200’displaysthedatafromtheUS‐sensorintheoutletchannel.

18

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

52

54

56

‐115 ‐95 ‐75 ‐55 ‐35 ‐15 5 25 45 65 85 105 125 145 165 185 205

Flow

height[mm]

Distancefromthrottle[cm]

Flowheights@differentrakes

Rake#1@06cms Rake#2@06cms Rake#2a@06cms Rake#3@06cms Rake#4@06cms WithoutRake@06cms





39

Thehighestdeviationscanbefoundinthevaluesatposition‘‐98’upstreamtherakes(Table6).

These are caused by the particular construction reducing the discharge section. Rake#2a and

Rake#3showedthebiggestbackwatereffectsatdischargescorresponding to12and14m³/s.

Thesewerealso theones tohavehorizontally installedbeamson the lowest level (cf.1.4).At

position‘‐10’and‘200’,thedeviationsshowvaluesbelow1.7mm,whichiswithintheaccuracyof

ourmeasurements.

Table6:Maximumdeviationofthewaterheightbetweendifferentrakesatparticulardischarges(valuesinmm).

Discharge Position to throttle

‐98,00 ‐10,00 200,00

06 m³/s 1,67 1,51 0,91

08 m³/s 2,55 1,56 0,70

10 m³/s 1,40 0,35 0,90

12 m³/s 2,74 1,64 1,25

14 m³/s 2,83 1,52 1,11

2.1.5 Effect of the inlet design and positioning of the rake

Eveniftherakestructurehasalittleimpactontheflowconditions,theshapeoftheinletandthe

distancebetweenrakeandthrottledo.Thisimpactwasobservedonconditionswithoutretention

ofwateratthethrottle,upto13.6m3/sinrealscale,respectively.

Inoursetup theoutlet channelwasextended30cmupstreamasaparallelchannel,before it

opened up towards the basin. The funnel leading into the parallel channel was hydraulically

optimized(seeFigure8orFigure19toFigure33)toguidethewatertothethrottle.

Thegreatestbackwatereffectswereobservedinthelastpartofthefunnel,justupstreamofthe

startingpointof theparallelchannelprofile.Theparallelprofileresulted inan increased flow

velocity.Ahighervelocitymeanslowerflowdepth(seeFigure41).So,themaximumdischarge

canbeincreasedbyoptimizingtheareaofacceleration,upstreamthethrottle.

Iftherakestructure‐independentfromthedesign‐wasinstalledtooclosetotheareaofflow

acceleration,firstbackwatereffectsatthethrottlecouldbeobservedatsmallerdischarges.

Forthecaseofanemptybasinahydraulicjumpwasobservedupstreamtherake.Dependingon

thedischarge itwasobservedat locationsbetweenabout205cm(at14m3/s)and150cm(at

6m3/s)upstreamthethrottle.Withapartiallysedimentfilledretentionbasintheseeffectswere

notobservableanymoreduetotheincreasedroughnessofthedepositedbedloadmaterial.

40

2.1.6 Length of the overfall

Figure42showsasketchofthenappeatthechanneloutlet.Thedistances(valuesinnaturalscale)

weremeasuredattheintersectionoftheupperandlowernappeandahorizontallineattheheight

ofthedownstreamboundarywallcrestofthestillingbasin.Themeasurementsweredoneon‘full

basin’conditions.ThevelocityshowninFigure42,wascalculatedbythewaterheightintheoutlet

channel (US_4 showed 1.23m water height, diameter of the outlet channel 3,05m) and the

discharge(45m3/s),anditwasmeasuredbyaflowmeteraswell(see1.3.8).

Calculationforthevelocity:

Theparametersv,QandAcorrespondto:

v,velocity(m/s)

Q,discharge(m3/s)

A,flowarea(m2)

ThecalculatedandmeasuredvelocitywasscaledfollowingthescaleratioafterFroude(see1.1).

Figure41:Inletdesignupstreamthethrottle.

41

Figure42:Sketchofthelongitudinalsectionofthenappeat'fullbasin'conditions.

2.1.7 Discharges at different storage levels

Figure43showsthecorrelationbetweenagivendischargeandthewaterlevelintheretention

basin.Theopeningheightatthethrottlewas1.3minnaturalscale.Themeasurementsweremade

3m (10cm in model scale) upstream of the throttle (position of the sensor US_5), so that

backwaterdidnotaffectthemeasurements.Thegivenvaluesrepresentthewatersurfaceheight

atthethrottle,measuredfromtheoutletchannelbottom.Thedatawererecordedatsteadystate

conditions.

Atransitionfromfreeflowtopressureflowoccursat13.6m3/sinnaturalscale.However,this

flowratecanoccuraseitherfreefloworpressureflowunderdifferentcircumstances.

Withrisingstagethewaterheightforarateof13.6m3/sisabout1.3m(naturalscale)underfree

flowconditions.Thefree flowcontinuesuntil the flowrateexceeds13.6m3/sor if the flowis

disturbed by, e.g. a tree reaching the rake. In the latter case backwater effects occur and the

storagelevelreachesaheightof4m(withasteadyflowof13.6m3/s).Onlyiftheflowleveldrops

belowthisrate,thestorageleveldecreases.

Ifthebasinisfilledandtheinflowdecreasesto13.6m3/sthestorageheightremains4muntil

theflowcontinuestodrop.

42

Figure43:Watersurfaceheightsatdifferentdischarges.

2.2 Experiments with woody debris

Teststoobservetheeffectsofthedifferentrakedesignswereperformedinordertoanalyzetheir

abilityofretainingwoodydebris.4typesofrakeswereusedforthistestbatch(Rake#1,Rake#2a,

Rake#3,Rake#4).Rake#2wasexcluded,becauseofitshighpermeability,duetothehighbasal

outletdesign.

2.2.1 Test setup

A discharge of 2.43l/s (12m³/s in natural scale) guaranteed a maximum of woody debris

transport,withoutbackwatereffects.Thethrottleopeningwith4.34cminthemodelremained

equaltothemaximumdischargeconditionsdownstreamthedam.

Roundbeechwoodstickswithalengthof140mmwasusedtosimulatewoodydebris.Thesticks

were split up in three different diameters: 6mm (‘S’ for small), 11mm (‘M’ formedium) and

15mm(‘L’forlarge).Accordingtothelowlevelflowconditionsupstreamoftherakes,thewoody

debriswassupplied110cmupstreamthethrottle(‘0’‐positionseeFigure13)inthemiddleofthe

channel.Foratestscenario4bundlesofstickswereused,including4S,4Mand2L.Forarandom

distributionofthewoodsticksoverthewholewidthofthechannelabundleofstickswasreleased

at40cmheight,stickbystickinaverticalorientation.Thereforeaspecifiedorder(M‐S‐L‐M‐S‐M‐

S‐M‐S‐L)inasequenceofaboutonesecondwasused.Duringonetest,4bundlesinasequenceof

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35 40 45 50

height[m

]

discharge[m3/s]

Dischargesatdifferentstoragelevels

freesurfaceflow

flowunderpressure

43

aboutoneminutewerebroughtin.Besidesthenumberandtypeofthestickspassingtheinstalled

rakewasrecorded.Foreachrakethetestwasrepeated5times.

Drybeechwoodhasasimilardensityasgreenspruce.Therefore,thesticksweredriedbetween

thesingletest‐runs.Table7showsthemeannumberofsticksandtherelatedstandarddeviation

thatpassedtherakefortheabove‐describedsetup(averageof5testsperrake).

Table7:Meannumberofwoodpiecesthatpassedtherake.

All woody debris that passed the rake was transported through the outlet channel without

depositionintheoutletchannelorclockingofthethrottle.

2.2.1.1 Rake#1

Onaverage4.8sticksoutof40passedrake#1.Itistheonlyraketype,werewoodofthecategory

Lpassed.AtypicalpatternofhowthewoodisretainedinfrontoftherakeisshowninFigure44.

.

Figure44:Woodydebrisinfrontofrake#1.

Woody Debris S M L Sum SML

Rake#1 Mean 1.2 2.6 1 4.8

Stan. Dev. 2.17 2.30 1.00 4.55

Rake#2a Mean 2 1.4 0 3.4

Stan. Dev. 2.35 1.67 0.00 3.85

Rake#3 Mean 0.8 0.8 0 1.6

Stan. Dev. 0.84 1.10 0.00 1.82

Rake#4 Mean 0.4 0.6 0 1

Stan. Dev. 0.55 0.55 0.00 0.71

44

2.2.1.1 Rake#2a

Onaverage3.4sticksoutof40passedrake#2a.Atypicalpatternofhowthewoodisretainedin

frontoftherakeisshowninFigure45.

Figure45:Woodydebrisinfrontofrake#2a.

2.2.1.2 Rake#3

Onaverage1.6sticksoutof40passedrake#3.Atypicalpatternofhowthewoodisretainedin

frontoftherakeisshowninFigure46.


45

2.2.1.3 Rake#4

Onaverageonly1.0stickoutof40passedrake#4.Atypicalpatternofhowthewoodisretained

infrontoftherakeisshowninFigure47.


2.2.2 Effect of rake designs

Thedriftwoodexperimentsshowthatalltypesofrakesfiltertheamountofdriftwood,butrake#4

seemstobethemosteffectiveforthemodeledscenario.Ithastobenoted,thatthesetestshave

been performed with an empty basin (no bedload deposition) and at a discharge, where no

backwater effects are present. Rakes#2a, 3 and 4 are evenmore effective,when the basin is

alreadyprefilled,becausethenthereisnomoreclearancebetweenthegroundandtherake.

2.3 Experiments with bedload transport

2.3.1 Setup

Forthebedloadexperiments,thewaterandsedimentsupplyforthemodelwasredesigned.The

channelstartedwithanarrow40cmwideand48cmlongchannel,followedbyawideningwith

an angle of 26° on both sides. This installation ensured a constant sediment transport. The

installedconveyorbeltprovidedthebedloadmaterialjustabovethemodel.Inthiswayconstant

bedloadtransportcouldbeguaranteed(seeFigure48).

46

Thesedimentthatpassedtherakewastransportedeasilythroughtheoutletchannel(seeFigure

49). The round channel profile and the higher velocity in the parallel profile ensure that the

materialisflushedthroughandpreventlogjamsatthethrottle.

Figure48:Retentionbasinwithtargetsforphotogrammetryandsupplyinstallationforthebedloadexperiments.

Figure49:Sedimenttransportafterrakestructure.

47

Forthegrain‐sizedistributionoftheaddedsediment,transectbynumberanalysesprovidedby

theTownofCanmoreatCougarCreekwereevaluatedafterFehr(1987)anddownscaledforthe

physical scale of themodel. The finest parts could not be considered for the physicalmodel,

becauseofthedifferentbehaviorofcohesivematerial.Acomparisonofthedownscaledgrain‐size

distributionoftheCougarCreekandthesedimentmixtureusedfortheexperimentsisshownin

Figure50.Thematerialhasadensityof2.65tons/m³.

Figure50:Comparisonofthedownscaledgrain‐sizedistributionandthesedimentmixtureusedfortheexperiments.

2.3.2 Experiments

Different scenariosweremodeled. First, the basinwas filledwith constant discharge (12m3/s

naturalscale)andbedloadtransport(0.14m³/snaturalscale)untilthebedloadmaterialreached

the rake. Then stereoscopic pictures had generated an elevation model. The discharge was

increasedstepwise, firstwithand thenwithoutbedloadaddition.Aftereachstepanelevation

model was generated and during the tests, sediment was trapped at the outlet of the outlet

channelandevaluatedfor1‐minuteintervals.Figure51toFigure58showthebedloadtransport

experiments.Thewaterdischarge(blueline)andthesedimentinput(purpleline)aswellasthe

sedimentoutput (magentabars) are shown.Thedepositionvolume in thebasinbasedon the

volumetric analysis is shown by hillshades. The related deposition volumes are shown in the

diagrams.

48

2.3.2.1 Experimental run BL4

Thisrunmodeledaprefilledbasin(untilT=50min),followedbytwosmallerfloodswithadditional

bedload.Thesequenceendedwith5floodpeakswithoutsedimentinputtoinvestigatetheself‐

emptyingbehavior(alldischargevaluesaregiveninFigure 52). For this experimental run all

discharge rates could pass the throttle without backwater effects. After about 115 minutes

sedimentpassedthroughtheoutletchannel.Allsedimentthatpassedthethrottlewastransported

throughthedam.Duringthewholeexperimentnomaterialwasdepositedintheoutletchannel.

Figure51showsthebehaviorofthedepositedmaterial.UntilthetimeT=100minthebasinwas

filled,thenerosionwasthedominantprocess.

Figure51:HillshadesofthebedloaddepositionatdifferenttimesforthebedloadtransportexperimentBL4.

49

Figure52:WaterandsedimentdischargeforthebedloadexperimentBL4.

2.3.2.2 Experimental run BL5_6

This runmodeledaprefilledbasin (untilT=60min), thenapeak flowwithadditionalbedload

followedbyahigherfloodevent.Anotherpeakflowwithadditionalbedloadpursuedthehigher

flood.Duringthehigherfloodbackwatereffectsatthethrottlewereobserved.Duringthistimeno

materialwastransportedthroughtheoutletchannel.Whenthedischargewasreducedagainno

morebackwatereffectswerepresent.Atthisstagesediment(T=250min)transportthroughthe

outletchannelstartedagain.Allsedimentthatpassedthethrottlewastransportedthroughthe

dam.Duringthewholeexperimentnomaterialwasdepositedintheoutletchannelanddeposition

wasthedominantprocess(compare:Figure55and Figure56).

AtthetimeT=150minbedloadmaterialaccumulatedinfrontoftherakeandthelevelofsediment

wasrising.Materialwasthendepositedbetweentherakeandthereachabovethethrottle.

50

This ledtoslightlyreduced ‘maximumdischarge’conditionsresulting inbackwaterconditions

(seeFigure53).Duetotheaccelerationatthethrottle,thethrottleitselfwasnevercloggedduring

theexperimentalruns(seeFigure54).

Figure55:HillshadesofthebedloaddepositionatdifferenttimesforthebedloadtransportexperimentBL5_6.

Figure53:Bedloadtransportthroughthethrottlereduces'maximumdischarge'.

Figure54:Throttleaftersuddenlystoppeddischarge.

51

Figure56:WaterandsedimentdischargeforthebedloadexperimentBL5_6.

2.3.2.3 Experimental run BL7

Therunmodeledaprefilledbasin(untilT=60min);thenashortpeakwithadditionalbedload,

followedbyasmallerpeakwithoutsedimentinput.Thiswasrepeatedthreetimes.Duringthe

short,higherpeaks,thebackwatereffectsatthethrottlewereobservedwithnosedimentpassing

the structure. The longer, lower peaks remobilized the depositedmaterial. All sediment that

passedthethrottlewastransportedthroughtheretentionstructure.Duringthewholeexperiment

nomaterialwasdepositedintheoutletchannel.

Figure57showsthebehaviorofthedepositedmaterial.Duringthefillingphase

andthehighdischargephasesdepositionwasthedominantprocess.Duringthephaseswithlower

dischargeerosiontookplaceinthebasin(seeFigure58).

52

Figure57:Hillshadesofthebedloaddepositionatdifferenttimesforthebedloadtransportexperiment BL7.

53

Figure58:WaterandsedimentdischargeforthebedloadexperimentBL7.

2.3.2.4 Effects in the stilling basin

Thebehaviorofwaterandsedimentinthestillingbasinwasdocumentedwithphotographs.

Thereweresomecharacteristicscenariostoobserve:

Discharges between 0 and 2.8l/s (14m³/s) delivered bedloadmaterial to the stilling

basin,whichwas thendeposited.Thehigherdischargesof this rangealso remobilized

materialinthestillingbasin,incaseofprefilledconditions.(compareFigure59andFigure

60)

54

When the discharge exceeded 2.8l/s, no bedload arrived at the stilling basin due to

backwatereffectson theother sideof the structure.The increaseddischargecauseda

remobilizationofmaterial(seeFigure61).

Figure59:DepositedMaterial. Figure60:Depositingandremobilizingmaterial.

Figure61:Remobilizingmaterialwithoutsedimentsupply.

Figure62:Dischargeof2.5l/s(12m³/sinnature). Figure63:Dischargeat'fullbasin'conditions.

InFigure62theflowbehavioratadischargeof12m3/sisshown.Bedloaddepositiontakesplace

in the not prefilled stilling basin. Figure 63 shows the same scenario, but under ‘full basin’

55

condition.Thewateroftheoutletchannelsplashagainstthedownstreamwallofthestillingbasin

andnobedloadtransportcanbeobserved.

2.4 Overflow scenario

For the overflow experiments, the downstream face of the dam structure was installed (see

chapter2.1.1.4).Severaldifferentsetupsweretested,including:

flowdividersattheintersectionoftheembankmentdamandtheoutletstructurefora

ventilationofthechannel;

baffleblocksonthedownstreamboundaryofthestillingbasintodissipateenergy;

chuteandbaffleblocksatthedamfoot,toinitiateahydraulicjumpclosetothedam;

differentheightsofthedownstreamboundarywallofthestillingbasin;

anddifferentdimensionsofthebasin.

2.4.1 Velocity distribution

Inorder togetavelocitydistributionover thedownstreamfaceof thedam(seeFigure64),a

rasterofmeasuringpoints,regularlyspreadover theareawasused.Themeasuringwasdone

using a flowmeter (see Figure 17 and Figure 65). At the lower quarter section of the dam

entrappedairconditionsoverthewholewidthofthedamfacewereobserved.Figure64shows

themeasuredvelocitydistribution.

56

Figure64:Measuredvelocitydistribution. Figure65:Velocitymeasurements@downstreamdamsurface.

2.4.2 Stilling basin

Figure66andFigure67showplotsofthestillingbasin,containingtheinstalledchuteandbaffle

blocks(grey).Whilethedamconstructionendedwiththeoutletofthechannelforpreviousmodel

runs,itwaselongatedfortheinvestigationswithoverflow(lilacinFigure66).Hence,thefootof

thestructurewaslocatedinthestillingbasin.Partsofthechuteandbaffleblockswereintegrated

inthestructure.

Figure66:Longitudinalsectionofthestillingbasin(dimensionsincm).

57

Figure67:Groundplotofstillingbasin,includingchuteandbaffleblocks(dimensionsincm).

Theeffectoftheblockswastheinitiationsofadirecthydraulicjump(seeFigure68),whereasthe

testswithoutblocksresultedinanelongatedhydraulicjump(seeFigure69).

Figure68:Stillingbasinwithoutchuteandbaffleblocks.

58

InFigure70itispossibletoseetheabove‐mentionedsetupat‘fullbasin’conditions.Inthiscase,

thechuteandbaffleblockstructureisnoteffectiveandthemainflowsplashesinthebasinand

againstthedownstreamboundarywall.Figure71showsthemodelon‘overflow’conditions;the

chuteandbaffleblocksareactivatedresultinginadirecthydraulicjump(seeFigure71).

Figure70:Stillingbasinon'fullbasin'conditions. Figure71:Stillingbasinon'overflow'conditions.

Figure69:Stillingbasinwithchuteandbaffleblocks.

59

Experiments, where the stilling basin was prefilled with bedload material showed, that the

sedimentwaswashedoutduringtheprocessoffillingtheretentionbasin(seeFigure72).While

runningthe‘overflow’conditions,mostofthesedimentwasremobilized,andalittleremainedin

avortex.

Behindtheretentionstructuresedimentationpatternswereobservedduringtheemptyingofthe

basinattheendofthe‘overflow’scenario.Theremainingmaterial,whichwasnotflushedoutof

thestillingbasin,wasrelocatedtothesidesoftheretentionbasin(seeFigure73).

Figure72:Startingatestwithprefilledstillingbasin. Figure73:ErosionofSedimentaftera'overflow'test.

60

2.5 Investigations on the diversion tunnel

Asecondoptionforabottomoutletofthedebrisfloodretentionstructurewasinvestigatedwithin

the detailed design phase. This option includes amined diversion tunnel leading through the

bedrockontheleftsideofthestructureincombinationwiththespillwayasdefinedinthebase

design.

Thephysicalscalemodelwasmodifiedtotestthehydraulicsituationinthetunnel,includingsuper

elevation of the flow and impacts for the design of the aeration system. The scope of work

included:

Investigations on the required throttle opening height for the design of the diversion

tunnel.

Determinationofthemaximumfreesurfaceflowforthechangeddesign.

Velocitydistributionalongthelongitudinalsectionofthediversiontunnel.

Determinationofsuperelevationinthetunnel.

Investigationsonthebehaviorofthesedimenttransportinthediversiontunnel.

2.5.1 Setup

Themodelasexplainedabovewasmodifiedforthediversiontunnel.Becausethediversiontunnel

modelwasnotintegratedinthebasemodel,thesetupandmeasuringmethodisdescribedinthis

chapter.

Thegivenspecificationsforthediversiontunnelinnaturalscalewere:

Aninnerdiameterofthediversiontunnelof4.5m.

Aninclinationof2.7%overthelongitudinalprofileofthetunnel.

Anarcradiusofthetunnelof86matthecenterofthediversiontunnel.

Atunnellengthof150m.

Thesamethrottleshapeasforthebasedesignwasusedforthetunneloptionwiththe

loweredge in thehorizontalposition.Theopeningunder the throttle leads to a semi‐

circularcrosssection.

Thestoragelevelstaysthesamewith29.85mwaterheadattheloweredgeofthethrottle.

Amaximumdischargeat‘fullbasin’conditionsof45m3/s.

Forthephysicalscalemodelahorizontalplatformwasbuiltonwhichatransparentflexibletube

wasplacedinthespecifieddimensionsandadjustment(seeFigure74).

61

Fromtheintermediatebasinatubingtransportedthewatertothediversiontunnel(flexibletube)

withthethrottleinstalledinsideattheupstreamend(seeFigure75).Tubesforpressureheights

wereconnectedtoobserveandcontrolthepressureheight.Thediversiontunnelstructurewas

fixedonasupportingprofilewithaninclinationof2.7%ontheplatform.Figure76showsaplan

viewofthetunnelmodel.

Figure76:Planview:diversiontunnelmodel(dimensionsincm).

Figure74:Platformandflexibletubeofthediversiontunnelmodel.

Figure75:Watersupplytothediversiontunnelmodel.

62

2.5.2 Hydraulic investigation

2.5.2.1 Throttle opening height

Forthehydraulicinvestigations,a‘fullbasin’experimentwasperformedtodeterminethespecific

throttleopeningheightforthisdesignforastoragelevelof29.85minnaturalscale(99.5cmin

modelscale).Thetestresultedinathrottleopeningheightof3.7cminthemodel(1.11mnatural

scale).

Figure77:Crosssectionofthediversiontunnelmodelatthethrottle(undefineddimensionsincm).

2.5.2.2 Maximum free surface flow

The opening area at the throttle changed from 33.15cm2 in the previous model to 33.9cm2

(2.98m2to3.05m2naturalscale).Theeffectofthisdeviationinthemodeliswithinthemeasuring

tolerance.Thus,itisassumedthatthemaximumfreesurfaceflowwillbethesameforthebase

designandthediversiontunnel,aslongastheinlethasthesameinclinationandhydraulically

convenientshape.

2.5.2.3 Super elevation

Forthesuperelevationinvestigations,thedischargeinthemodelwassetto9.13l/s(45m3/sin

naturalscale).Thetransparenttubeallowedtotracethewaterheightatthelongitudinalsection

at the innerandouterradiusof thediversiontunnel.Thepictures inFigure78showthe flow

conditionatthespecificdischargesatthepositionofthehighestsuperelevation.Thesocreated

linesweremeasuredandprojectedtothecenterradiusofthetunnel,ascanbeseeninFigure80.

63

Atsteadystateconditionswithadischargeof9.13l/smodelscale(45m3/snaturalscale), the

pointofthehighestsuperelevationwasreachedat88cmdownstreamofthethrottleinthemodel

(26.4mnaturalscale).Laterintheflowthesuperelevationdecreased.At175to214cm(52.5to

64.2m innaturals scale)downstreamof the throttle the super elevationwas about zero, and

increased again to a secondpeak at 262cm (78.6mnatural scale) and a third one at 398cm

(119.5mnaturalscale)downstreamofthethrottle.Thevaluesforthispeaksinnaturalscaleare

showninTable8.

Table8:Valuesforthethreepeaksofthesuperelevationinnaturalscale.

Positiondownstreamofthethrottle[m]

Waterheightattheouterradius[m]

Waterheightattheinnerradius[m]

Superelevation[m]

26.3 3.5 0.4 3.1

78.7 3.2 0.6 2.6

119.5 2.4 0.9 1.6

Figure78:Thepointwiththehighestvalueofsuperelevationsatthestateddischarges(naturalscale).

64

2.5.2.4 Energy heights

Experiments to investigate the energy heights in the diversion tunnelwere run at ‘full basin’

conditions(45m3/sdischargeinnaturalscale)togetinformationabouttheworstcasescenario.

Observations on the hydraulic conditions in the tunnelwas done at 16 locations. Thesewere

locatedatthemainpointsofinterest,likethehighestandlowestpointsofthesuperelevation,the

upstreamendofthetunnel,directlyatthethrottle,upstreamofthethrottleandatthehalfdistance

inbetweenthepointsofthehighestandlowestsuperelevation.Themeasuringpositionsofthe

tunnelmodelareshowninFigure76.

Attheselocationsthewaterheightsweremeasuredbyametalstickmeasuringthedistancefrom

theupperedgeofthetunneltothewatersurfaceunderdifferentangles.Togaintheinformation

aboutthewatersurface,thesedatawereimportedtoAutoCADandprocessedtoseethedifferent

formsofwatersurface.Thepointsof thehighestand lowestwaterelevationareshowninthe

upperdiagramofFigure80.Thecorrespondingflowarea(comparabletoflowconditionswithout

superelevations)wascalculatedtodeterminethedifferentvelocitiesandpressureheights.

AfterBernoullithetotalEnergyheadEcanbecalculatedforeverymeasuredcross‐section:

²2

Wherezistheelevationofthechannel,yistheflowdepthandv²/2gisthevelocityheadwithv

beingthevelocity(seeFigure79).

65

Figure79:Energylineforopenchannelflow(fromCIVE24002008).

With increasing distance from the throttle itwas possible to observe decreasing velocity and

energyheight(seelowerdiagramatFigure80).

Table9showsthecalculatedvelocityforthecertainpositions.AscanbeseeninTable9andFigure

80 (Energy grade line diagram) there are rising values at the positions of the highest super

elevations.Thiseffectcanbeattributedtoentrappedair,whichmayfalsifythemeasurementat

thispositions.

Table9:Velocitydistributionatthelongitudinalsectionofthediversiontunnelinnaturalscale.

Distance from throttle [m] Calculated velocity [m/s]

‐3 2,83

0 24,61

6,049 22,00

16,158 19,31

26,268 19,85

43,931 17,36

61,594 15,57

69,020 14,90

76,446 15,58

89,466 14,25

102,486 14,09

109,727 14,18

116,969 14,43

130,798 12,54

144,628 12,30

66

Figure80:Diagramincludingcrosssections,superelevationandtheenergygradelinesatthelongitudinalprofileofthediversiontunnel(valuesinnaturalscale).

67

2.5.3 Sediment transport investigation

Toexploreapossiblesedimentdeposition in thediversiontunnel,experimentswithsediment

weremade.Thebasedesignexperimentsshowedamaximumsedimenttransportof0.032kg/s

in model scale (see Figure 58), what correspond to 0,06m³/s in natural scale. For the

investigationsonthediversiontunnelmodelthis0.032kg/swereusedfortestswithdischarges

from1.2to9.13l/s(6to45m3/snaturalscale):Thegrainsizedistributionofthesedimentwas

thesameasinthe‘experimentswithbedloadtransport’,theinputpositionwasjustdownstream

ofthethrottle.

The experiments showed that all the sediment was transported through the tunnel and no

sedimentationwithinthetunnelwasregisteredatalltesteddischarges.Figure81andFigure82

showthesedimenttransportattheendofthetunnelatthestateddischarges.

Figure81:Sedimenttransportat6m3/snaturalscale.

Figure82:Sedimenttransportat14m3/snaturalscale.

68

3 Conclusions and Recommendations

3.1 Hydraulic experiments

Withthe ‘fullbasin’experiment,anthrottleopeningheightof4.3cm,respectively1.3minreal

scalewasdeterminedfortheroundchanneldesignwithandiameterof3minrealscale.

For this throttle opening the ‘maximumdischarge’ test showedadischargeof 2.75 l/s,which

means 13.6m³/s for real conditions, that can pass the retention structurewithout backwater

effects.

Thethrottledesign(45°versusstraightedge)didnotinfluencethedischargesignificantly.

None of the tested rake type influenced the discharge through the structure at ‘full basin’

conditions. The ‘maximum discharge’ was not influenced by the rake as long as the distance

betweentherakeandthrottlewassufficient.Iftherakestructure,independentfromthedesign,

wasinstalledtooclosetotheareaofflowacceleration,firstbackwatereffectsatthethrottlecould

beobservedatsmallerdischarges.

Therakeswithhorizontalbeamsatthelowerleveloftherake(Rake#2aandRake#3)increased

thebackwatereffectoftherakeslightlyatthemostupstreammeasuringposition.Belowtherake

structure,therewasnosignificantinfluenceoftherakeontheflowconditions.

Whentheretentionstructurewasfilledwithwater,uptothedamcrest,andthethrottleopening

was1.3m,thevelocityinatthelowerpartoftheoutletchannelwasaround16m/s.Thenappe

showedadistancefrom4.5mto11.4mfromtheendoftheoutletchannel.Thesedistanceswere

measuredontheheightofthedownstreamwallcrest.

3.2 Experiments with woody debris

Thedriftwoodexperimentsshowedthatalltestedtypesofrakesreducetheamountofdriftwood

byatleast90%,butrake#4seemstobemosteffectiveforthemodeledscenario.Ithastobenoted,

that these tests have been performedwith an empty basin (no bedload deposition) and at a

dischargewithnobackwatereffects.Rakes#2a,3and4areevenmoreeffective,whenthebasin

isalreadyprefilled,becausethenthereisnomoreorsmallerclearancebetweenthegroundand

therake.Assoonasbackwatereffectsarepresentit isveryunlikelythatdriftwoodpassesthe

rake,becauseofthereducedflowvelocityinfrontoftherake.

69

3.3 Experiments with bedload transport

3.3.1 Deposition behavior and remobilization of material

Fortheexperimentsstartingwithemptybasinconditionsthebedloadlayerhadtoreachtherake

first,andthenthematerialwaspartlytransportedthroughtherakeandpassesthethrottle(under

naturalconditionssedimentisavailableimmediately).Assoonasbackwatereffectswerepresent

alladdedmaterialwasdepositedinthebasin.Whennormalflowconditionswerereachedagain

(nobackwateratthethrottle)thedepositedmaterialwasremobilizedagain.Withoutadditional

bedload,erosionwasthedominantprocessinthedepositionbasin.

3.3.2 Bedload transport in the outlet channel

Innoneoftheexperimentsdepositionintheoutletchanneltookplace.Allmaterialthatpassed

thethrottlewastransportedthroughthedam.Forthecaseofhighbedloadtransportandstarting

backwaterconditionsmaterialwasdepositedbetweentherakeandthereachabovethethrottle.

Due to the acceleration at the throttle, the throttle itself had never been clogged during the

experimentalruns.

3.3.3 Bedload deposition/erosion behavior in the ‘stilling basin

Experiments,wherethestillingbasinwasprefilledwithbedloadmaterialshowedthatdeposition

takesplaceatdischargesfrom0to13,6m3/s(‘normalflow’conditions).Higherdischargesofthis

rangealsocauseda remobilizationof sediment,when thebasinwascompletely filledupwith

sediment.Dischargeshigherthan13,6m3/s(showingawaterretentionupstreamthedam)ledto

mobilizationofsedimentintheretentionbasin.Whilerunningthe‘overflow’conditions,mostof

the sediment was remobilized, and a little remained in a vortex. During the emptying of the

retentionbasinfollowingthe‘overflow’scenario,theremainingmaterialwasmovedtothesides

oftheretentionbasin.

3.4 Overflow

Theexperimentsshowedthatthetestedchuteandbaffleblocksareveryeffective.Thechuteand

baffle blocks initiated a direct hydraulic jump in the first sector of the stilling basin during

‘overflow’conditions,whereasthetestswithoutblocksresultedinanelongatedhydraulicjump.

Butinthecaseof‘fullbasin’conditions,thechuteandbaffleblockstructurewasnoteffectiveand

themainflowsplashedinthestillingbasinandagainstthedownstreamboundarywall.

70

3.5 Diversion tunnel option

Asecondoption for thebottomoutletwasspecifiedasadiversion tunnel leading through the

bedrock on the side of the structure. The tunnel in natural scale has a diameter of 4.5m, an

inclinationof2.7%,aradiusof86mandalengthof150m.

Forthissetup,athrottleopeningheightof1.11mnaturalscalewasdetected,themaximumfree

surfaceflowwasthesameasinthetestswiththeoutletchannel(13.6m3/snaturalscale).

The super elevation reached amaximum of 3.1m, 26.2m (natural scale) downstream of the

throttle. At this position thewater height in the diversion tunnel at the outer radius is 3.5m

(naturalscale)overthetunnelbottom.Thewaterdidnotreachthetopofthetunnel.

Thenaturalscalevelocityrangewascalculatedwith24.6m3/s(highestvalue)atthethrottleto

12.3m3/s(lowestvalue)at144.6mdownstreamofthethrottle.

Investigationswithbedloadtransportshownodepositionofsedimentinthediversiontunnelfor

thetestedsetup.

3.6 Scaling issues in hydraulic modelling

AccordingtoTaveiraPinto(2012)differencesbetweenthemodelandtheprototypebehaviormay

occurduetoseveralreasons;however:

Scaleeffectsarealwayspresent.

Thebiggerthescalingfactor,thelargerwillbethescaleeffects.

Scaleeffectsdonotaffectallphenomena/parametersunderinvestigationinthesameway

– qualitatively theymay be reproduced differently betweenmodel and prototype, but

quantitativelytheycanbeproperlyscaled(dischargevsairentrainment).

Ingeneralsomeparametersaresmallerinthemodelthaninprototype–relativewave

height,relativedischarge,transportedrelativevolumeofsand,etc.

Froudesimilarityisnormallyconsideredinopen‐channelhydraulics,wherefrictioneffectsare

negligible(deep‐waterwavepropagation)orforhighlyturbulentphenomena,sincetheenergy

dissipationdependsmainlyontheturbulentshearstressterms.Statistically,thesearecorrectly

scaled even though the turbulent fine structures and the average velocity distribution differ

betweenthemodelandprototypeflows.Thegravitationalaccelerationisnotscaledaswellasthe

othernumbers.

Thereforeup‐scaledmodelresultshavetobeinterpretedcarefully.

71

4 References

ALPINFRACONSULTING+ENGINEERINGGMBH(2015).MountainCreekHazardMitigation,

Designofmitigationmeasures,CougarCreek.InterimReport03:FinalOption

Analysis.DatedfromJanuary2015.

BGCENGINEERINGLtd.(2014).CougarCreekdebrisfloodhazardassessment.Finalreport

revisedpreparedfortheTownofCanmore.DatedfromJune2014.

CANMORE(2015a).AboutCanmore,MountainCreekHazardMitigation.In:TheTownof

Canmore[online].Dateofconsulting:18/08/2015.Availableon:

http://www.canmore.ca/

CANMORE(2015b).CougarCreeklong‐termmitigation,Optionanalysissummaryreport.

CougarCreekOptionSelection.DatedfromJanuary2015.

CIVE2400FluidMechanics(2008).Section2:OpenChannelHydraulicsbyDrGoodwillandDr

Sleigh,UniversityofLeeds,SchoolofCivilEngineering.

PEPPERL+FUCHSGROUP,2014.UltrasonicsensorUC500‐30GM‐IUR2‐V15.Instructions.

PREIßLERG.andBOLLRICHG.(1985).TechnischeHydromechanik/1.VerlagfürBauwesen,

Berlin,2ndEdition.Pages299and500to505.

Preissler, G.; Bollrich, G.; Martin, H. (1989): Technische Hydromechanik. Band 2: Spezielle

Probleme. Berlin: Verlag Bauwesen

ROCKWELLAUTOMATIONInc.(2015).UltrasonicAdvantagesandDisadvantages.In:

RockwellAutomationInc.[online].Dateofconsulting: 15/07/2015.Availableon:

http://www.ab.com/

TAVEIRAPINTOF.(2012):ScalingIssuesinHydraulicModelling,Dateofconsulting7/06/2016.

Availableon:http://www.coastalwiki.org/wiki/Scaling_Issues_in_Hydraulic_Modelling

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