EffectofVegetationonDebrisFlowInitiationConceptualisationandParameterisationofaDynamicModelforDebrisFlow

InitiationinTikovilRiverBasin,Kerala,India,usingPCRaster

SekharLukoseKuriakoseJanuary,2006

EffectofVegetationonDebrisFlowInitiationConceptualisationandParameterisationofaDynamicModelforDebrisFlowInitiation

inTikovilRiverBasin,Kerala,India,usingPCRasterby

SekharLukoseKuriakoseThesissubmittedtotheInternationalInstituteforGeo-informationScienceandEarthObservationandtheIndianInstituteofRemoteSensing(NRSA)inpartialfulfilmentoftherequirementsforthedegree

ofMasterofScienceinGeo-informationScienceandEarthObservation,Specialisation:(HazardandRiskAnalysis)

THESISASSESSMENTBOARD

Prof.FreekvanderMeer,ITC(Chairman)Prof.R.C.Lakhera,IIRSDr.P.K.Champatiray,IIRS

Dr.R.K.Mazari,WadiaInstituteofHimalayanGeology

(ExternalExpert)

SUPERVISORS

ITC IIRSProf.R.CLakhera

ScientistSGIn-charge,GeosciencesDivision

CESS

Dr.CeesJ.vanWestenAssociateProfessorDrs.DinandAlkemaLecturerDepartmentofEarthSystemsAnalysis

Mr.G.SankarScientistE-2

ADVISORSUtrechtUniversity,DepartmentofPhysicalGeography

Dr.L.P.HvanBeekPostDoctoralFellow

Dr.T.W.J.vanAschLecturer(Retd)

INTERNATIONALINSTITUTEFORGEO-INFORMATIONSCIENCEANDEARTHOBSERVATIONENSCHEDE,THENETHERLANDS

ANDINDIANINSTITUTEOFREMOTESENSING(NRSA)

DEHRADUN,INDIA

Thisresearchwasmadepossiblewiththefinancialsupportfrom

InternationalTropicalTimberOrganization(ITTO),Japan

Disclaimer

This document describes work undertaken as part of a programme of study at theInternationalInstituteforGeo-informationScienceandEarthObservationandIndianInstituteof Remote Sensing (NRSA). All views and opinions expressed therein remain the soleresponsibilityoftheauthor,anddonotnecessarilyrepresentthoseoftheinstitutes.

SekharL.K

Dedicated to my beloved grandfather Rev. Fr. C.T Kuriakose, B.A, B.T, B.Ed

who turned 101 this year.

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Abstract

Debris flows,also referred toasmudslides,mudflows,ordebrisavalanchesareacommontype of fast-moving landslide that generally occurs during intense rainfall onwater saturated soil.Vegetation is an important factor influencing the occurrence of rainfall-triggered landslides. Thestudy attempts to numerically simulate the transient hydrological conditions and resultant slopeinstabilityconditionsoccurring inTikovilRiverbasinofKerala,and therebyquantify theeffectofvegetationontheinitiationofdebrisflowsintheregion. Modelling debris flow as a complete phenomenon is complicated.The present endeavourwastomodelonlytheinitiationconditionsthatarecausativetodebrisflows.Themodelusedforthestudy was STARWARS+PROBSTAB (van Beek, 2002) and is realized in the PCRaster(www.pcraster.nl)environment,arasterbasedGISpackage.Itisacoupledmodelthatconsidersbothhydrologicalandmechanicaleffectsofvegetationonslopeinstability.Themodellingresolutionwas20by20meters.DigitalTerrainModeloftheareawascreatedwithdatafromreliablesources.Initialconditionswerecomputedusingaverageseasonal rainfalldata from1965 to1999onaquarterdaytime step soas toachievenumerical stability.Thehydrologymodel simulatesvolumetricmoisturecontent and perched water level, while the slope stability model simulates factor of safety andprobability of failure. The model was modified based on debris flow initiation concept deemedpertinent to the study area; additional parameters such as root induced cohesion and vegetationsurcharge were incorporated; parameters that were originally not considered in themodel. Fieldmeasurements of root tensile strength and root shearwere conducted to account for root-inducedcohesionusinganempiricalequationsuggestedbyresearchersfromUSGeologicalSurvey(Schmidtet al., 2001). Hydrological Effects of vegetation such as interception and bulk throughfall werecomputedfromMODISderived16-daycompositeNDVIdata.InterceptionwascomputedforeverydayusingAstonsequation(Aston,1979)and throughfallwasaccountedassuggestedbyvanBeek(2002).ReferenceEvapotranspiration (RET)was computedusingHargreavesmethod as it showedmorecorrelationthanPenman-MonteithcalculatedRETtoobservedopenpanevaporationdata.RETwas later adjusted toActual Evapotranspiration usingCrop Factors derived from FAODatabase.Calibrationwas carried out using observed groundwater height data for the area.Resultant slopestabilityresultswerevalidatedfortheyears2000-2001.Validationofthemodelresultswerecarriedoutusingobservedlandslideinitiationlocationinformation. The model indicated that the vegetation of the region under consideration significantlyinfluences transient hydrological conditions leading to debris flow initiation and the hydrologicaleffects contributes inmaintaining the stability of the region in a long run.Root induced cohesioncontributes significantly inmaintaining the slope stability of the region.Surcharge is of relativelylessersignificanceintheoverallstabilityoftheregion. Itiscouldalsobeconcludedfromthestudythatphysicallybasedspatialmodelsareidealtoquantitativelyunderstand thecontributionofa specificparameter towardsdebris flow initiation,asprovedfromthestudy.Satelliteremotesensingdataderivedparameterisationsofhydrologicalmodelshaveapromising future in thepreviewof increasingspatialand temporalcoverage.EnvironmentalModellingLanguagessuchasPCRasterthataredistributedongratisforscientificstudiesarereliablealternativestoexpensiveonessuchasIDLforeconomicallydevelopingcountriesasIndia.

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Acknowledgements

IexpressmysincerethanksandgratitudetoDr.CeesJ.vanWestenandProf.R.CLakheraforbeingmyfirstsupervisorsandlightingawayformethatiscurrentinearthsciences.WordsarenotenoughtoexpressthegratitudetoDr.RensvanBeekforspendinghisvaluabletimeinadvisingmeallthroughthethesisworkanddirectmeineverysteptowardsachievingthegoals.IthankMr.G.Sankarforbeingmysupervisorandespecially inspendinghis timeandefforts in thefieldwithmeandprovidingaccesstoaplethoraofdata.Dr.Thw.vanAsch,inspiteofabusyschedulespenthisvaluable timeonadvisingme, I thankhim forhisvaluablecommentsrightfrom theproposalstageand Ihope Icoulddo justice to the time thathehasspentforme.I thankDrs.DinandAlkemaformotivating and guiding me to learn the fundamentals of dynamic modelling and especially forenablingmetoacquireenoughskillsinPCRaster. IthankDr.V.HariPrasad,ProgrammeCoordinator(HRACourses),IIRS,forstandingfirminhissupporttomyresearchaspirations.Withouthisconstantguidanceandadvisesitwouldnothavebeenpossible toevenenvisagesucharesearchwork.Mysincere thanksandgratitude isdue toDr.Paul.M.vanDijk,ProgrammeDirectorandAssistantProfessor,ITCforallowingmetoreturntoITCandcarryoutthemodellingpartofthestudyalongsidemysupervisorsandadvisors.ThanksareduetoDr.V.KDadhwal,Dean,IIRSforallowingmetopursuethecourseattheinstitute. TheadvicesanddirectionsprovidedbyDr.DavidG.Rossiter,AssociateProfessor,ITCandDr.P.KJoshi,Scientist,FED, IIRSwereofboundlessvalue;I thank them,for the timeandeffortsthattheyputinprovidingmewithinsightsintoachievingmygoals. IcannotforgetthelengthymailsandtelephonicdiscussionsthatIhadwithoneofmyverybestfriends,Ms.ShruthiB.V,IIScBangalore,whichdevelopedfurtherintomanysectionsasdealtinthethesis.ShewasaconstantmotivationandsupportandIthankherforthesame. Thanksandgratitude isdue toMr.SamVarghese, JRF, IIRS forbeingmy roommateandsucha lovingpersonwhoalways tookcareofmyneedswhenever Ineeded. Ialso thankMr.N.VLele,JRF,IIRSfortheintelligentsuggestionsandcontributionsofhisinthethesiswork. IthankDr.M.Baba,Director,CESSforlettingmeworkintheinstitution.IalsothankMr.JohanMathai,Scientist,CESSforallthesupportthatheprovidedwhileIwasattheinstitution.Mysincere thanks are due toMr. B. Sukumar andMrs. Ahalya Sukumar, Scientists, CESS for thevaluablediscussionsthattheyhadwithmeonmyresearchtopic.ThanksareduetoMr.S.Sidharthan,Scientist,CESSforprovidingmewiththemostcrucialdatasetsforthestudy. Thesupportprovidedby theRubberResearchInstituteofIndia,KottayamandKurisumalaChristianMonasterycannotbe ignored. Theclimaticdatasourcedfrom these two institutionswerecrucialfortheresearchandIthankthemforprovidingmethedata.Ithanktwoofmyfriends,Mr.S.Devavrathan, Project Associate, CESS andMr. JavedMalick, Student,M.Sc Geoinformatics inmorallysupportingmethroughthecrucialphasesoftheproject. ThanksarealsoduetoMr.RajuFrancis,Mr.SunilSahadevanandMr.AnilAntony,RangeOfficers,KeralaStateForestsandWildlifeDepartmentforbeingmyfriendsandlettingmerelaxevenwhen Iwas in a hot seat. I also thankMr.AsokSekhar,M.TechStudent, IIRS andMr.PrasanthNarayanan,JRF,SACONforbeingmyfriends.

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Tableofcontents ListofTables................................................................................................................................................. v ListofEquations.......................................................................................................................................... vi ListofFigures ............................................................................................................................................. vii1. Introduction .................................................................................................................................................. 11.1. DebrisFlows............................................................................................................................ 11.2. ProblemStatement................................................................................................................... 21.3. AimandObjectives ................................................................................................................. 31.3.1. ResearchQuestions.......................................................................................................... 31.3.2. ResearchHypothesis........................................................................................................ 3