labor & engenho l&e - ufrgs · labor & engenho v.9, n.4, p.76-89, out./dez. 2015....

Labor & Engenho v.9, n.4, p.76-89, out./dez. 2015.

L&E ISSN 2176-8846

Historicalanalysesofdebris1lowdisasteroccurrencesandoftheirscienti1icinvestigationinBrazil

DOSSIERDASÁGUAS:GESTÃODOPATRIMÔNIOHÍDRICO

MasatoKobiyamaProfessor.InstituteofHydraulicResearch,FederalUniversityofRioGrandedoSul.PortoAlegre[RS]Brazil.<[email protected]>.GeanPauloMichelSanitaryandenvironmentalengineer.PhDstudentofWaterResourcesandEnvironmentalSanitation.InstituteofHydraulicResearch,FederalUniversityofRioGrandedoSul.PortoAlegre[RS]Brazil.<[email protected]>.ElisieleCardozoEngsterUndergraduatestudentofGeography.InstituteofHydraulicResearch,FederalUniversityofRioGrandedoSul.PortoAlegre[RS]Brazil.<[email protected]>.MaurícioAndradesPaixãoUndergraduatestudentofEnvironmentalEngineering.InstituteofHydraulicResearch,FederalUniversityofRioGrandedoSul.PortoAlegre[RS]Brazil.<[email protected]>.

AbstractConsideringthedebrisflowashighly-destructiveflowofwaterandsedimentmixtureinawaywhereitisagravity-governedcontinuousflow,thepresentpaperconductedaWebsurveyoftechnical-scientificstudiesthattreatedthesephenomenawhichoccurredinBrazilduringtheperiod1900-2014.Althoughtheincreaseof occurrence from the 1990s caused the increase in the number of publication, there are still a smallnumber of publications, especially in scientific journals. A historical analysis about Brazilian studiesdemonstratesanactualsituationinBrazilandconfirmsvariousnecessaryandurgentactions.Amongthem,themoreimportantactionsare:(1)establishmentofterminologyandconceptaboutdebrisflowinBrazil;(2) systematization of hydrometeorological monitoring and topographic survey; (3) registration ofoccurrencesanddata-baseconstruction;and(4)developmentofwoodydebrisflowresearches.

KeywordsDebrisclow,scienticicresearches,history.

KOBIYAMA,M.;MICHEL,G.P.;ENGSTER,E.C.;PAIXÃO,M.A.HistoricalanalysesofdebrisclowdisasteroccurrencesandoftheirscientificinvestigationinBrazil.Labor&Engenho,Campinas[SP]Brasil,v.9,n.4,p.76-89,out./dez.2015.http://www.conpadre.org

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1.Introduction

Debris flows have been increasingly causing serious damages to the human society and theenvironment in theworld includingBrazil. This fact indicates the importance of developingmorescientific researches to understand the mechanisms of such natural phenomena and thecountermeasures required to reduce related disasters. In these circumstances, the InternationalConferenceonDebris-FlowHazardsMitigation:Mechanics,PredictionandAssessmentwasheldinSanFrancisco(USA)in1997,Taipei(Taiwan)in2000,Davos(Switzerland)in2003,Chengdu(China)in2007,Padova(Italy) in2011,andTsukuba(Japan) in2015.Asimilareventcalled InternationalConferenceonMonitoring,Simulation,PreventionandRemediationofDenseandDebrisFlowwasconductedfourtimes:inRhodes(Greece)in2006,NewForest(England)in2008,Milano(Italy)in2010andDubrovnik(Croatia)in2012.

Previously,scientistswhodevotedthemselvestothestudyofdebrisclowshadnoopportunitytoseethisaliveandrealphenomenondirectly.Thustheinformationwasdrawnthroughtestimonyfromafewwitnessesandobservationsofthedepositionareaofthedebrisclowafteritoccurs.Itmeans that, in fact, scientists could just imaginehow the clowdeveloped.Okuda et al. (1977)showed for the cirst time theworld a cilm of a debris clow,which signicicantly facilitated theunderstandingofitsmechanisms.Inthissense,thecontributionofOkuda'sworkandhisgroupwasdeextremeimportance.

Theworkentitled"Debrisflows"ofTakahashi(1991),publishedintheseriesofmonographsoftheInternationalAssociationofHydraulicEngineeringandResearch–IAHR,wasthefirstbookwrittenintheworldthatexclusivelyaddressedthisphenomenonsystematicallyandwasamajorstimulusto scientific community. Today there aremany books dealing only with this phenomenon (e.g.,MICHIUE&ARMANINI,1997;JACOB&HUNGR,2005;TAKAHASHI,2007),aswellasreviewarticles(INNES, 1983; DAVIES et al., 1992; HUTTER et al., 1996; COUSSOT&MEUNIER, 1996; IVERSON,1997;IVERSONetal.,1997;HUNGRetal.,2001;VANDINE&BOVIS,2002;TAKAHASHI,2009).

Analyzingdisastersrelatedtolandslides,Petley(2012)andSepúlveda&Petley(2015)showedatrendwhere countrieswith a large number of scienticic papers treating landslides suffer lessfrom thesedisasters. It implies thatBrazilian society alsoneeds to go further in their studiesaboutdebrisclowsinordertoreducethedisasterscausedbythem.

Therefore,theobjectiveofthepresentstudywastoinvestigatetheconceptofdebrisflowandtoperformahistoricalandquantitativeresearchontechnicalandscientificpapersdealingwiththisphenomenoninBrazil.AccordingtoAlexander(1989),thedebrisflowisthemostdestructivetypeamongallthetypesofmassmovements,andisresponsibleformoredeathsintheurbanarea.ThiscommentisprobablystilltrueinBrazilandintheworld.

2.Terminologyandconcepts

Takahashi(2007)definedthedebrisflowas“aflowofsedimentandwatermixtureinamannerasifitwasa flowof continuous fluiddrivenbygravity”, andcommented that suchaphenomenonhasgreat mobility. According Iverson (2004), the debris flow is a transitional phenomenon of massmovementwhosecharacteristicswerealternatedbetweenslippingandflooding.Coussot&Meunier(1996)consideredthat thedebris flowisan intermediatephenomenonamonghyperconcentratedflow and landslide. Precisely because of its transitional or intermediate characteristics, there arevariousdefinitionsandconsequentlyinaccuracies.

Owingtotheflowandtransitionnature,severalstudieshavesoughttodifferentiatebetweendebrisflows and other similar ones. For example, Costa (1988) attempted to differentiate debris flows,hyper-concentratedflowsandfloods.Imaizumietal.(2008)differentiatedlandslideanddebrisflow.Ofany form, thereareseveralattempts toestablishconceptsrelated to thisphenomenon.Table1showssomeexamples.


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Table1.Differentconceptstodecinethedebrisclows.

Thedebrisflowisverycommoninmountains.Consequentlythereareseveralwordstocallit.InJapan,peoplecallitja-nukewhichisanimageoflargesnakedestructingvalley,doseki-ryumeaningsoil-rock flow, yama-tsunami meaning mountainous tsunami, and so on. In Brazil, the termscorrespondingtodebrisflowarediverse,consistingofacombinationoftermswhichreplacetheword flow (fluxo/corrida/movimento/torrente) and theword debris (detritos/escombros/massa),i.e.,fluxodedetrito,fluxodeescombros,corridademassa,amongothers.Thuseveninonecountrytherearediverseterminologies.

Indeed, it is necessary todiscuss the characteristics of the flowingmaterial, i.e., debris.Hungr et al.(2001)defineddebrisaslooseandnon-uniformmaterialwithlowplasticity.Texturally,thedebrisisamixtureofsand,pebbles,bouldersandsilt.Frequently,thedebriscancontainorganicmaterialssuchastrunks,branches,amongothers.AccordingtoCruden&Varnes(1996),therearetwotypesofmaterialsthatconstituteflows:debrisandland.Thedebrisissoilcontainingstonesandothercoarseparticlesizesinahigherproportionthan20%,whilethelandswouldconsistofthisproportionlessthan20%.

Asdebris flowisaphenomenoncausingdisasters, itcanbehandledfromthepointofviewofnaturaldisastersandprotection/civildefense.In2008,theEmergencyDisasterDataBase(EM-DAT)oftheCentreforResearchontheEpidemiologyofDisasters(CRED)whichisthepartneragencyoftheWorldHealthOrganizationreclassifiedthedisasterstypesintotwomajorgroups:naturalandtechnological(SCHEURENet al., 2008).Naturaldisastersweredivided into six sub-groups: biological, geophysical, climatological,hydrological,meteorological and extraterrestrial (meteorites), and these, in turn, into twelve subtypes.Thisnewclassificationwastheresultofaninitiativebetweenthetwomaindisasterdatabases,theCREDandtheMunichReinsuranceCompany(MunichRe),whichdecidedtoadoptacommonclassificationfortheirrespectivedatabases(BELOWetal.,2009).

Themainchangewastheseparationofthemassmovementsintotwotypes:dryandwet.Thefirstisassociatedonly togeophysicalevents (earthquakesanderuptions)and thesecond tohydrological


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Authors Concepts

Varnes(1978) Flowistherapidmovementofviscousmaterial.Therearedebrisclow,mudclowandrocksavalanche,dependinguponthenatureofthematerialinvolvedinthemovement.

Costa(1988)Thedebrisflowisavisco-plastic,non-Newtonianfluidordilatantfluidinlaminarmanner,withuniformprofileofsedimentconcentration.Thesedimentconcentrationvariesfrom70to90%byweight(47to77%byvolume).Theshearstressisgreaterthan400dyn/cm2.

Jan&Shen(1997)Debrisclowsisagravityclowofmaterialcomposingamixtureofsoil,rock,waterand/orair,comingfromlandslidewithlargeamountofrunoff.Theirpropertiesvaryaccordingtotheamountofwaterandclay,thesedimentsizeanditsdistribution.

USGS(1997)Debrisclowsarefast-movinglandslideswhichoccurinvariouspartsoftheworld.Theyareparticularlydangeroustolifeandproperty,becausetheyabruptlymoveanddestroyobjectsontheirpath,andoftenoccurwithoutwarning.

Vandine&Bovis(2002)Thedebrisclowisatypeofmassmovement,whichinvolvestherapidmovementoforganicandinorganicmaterials(predominantlycoarsematerial),saturatedwithwaterandalongconcinedandslopingchannel.

Imaizumietal.(2008) Massmovementsaredividedintotwotypes:slopesandchannels.Themovementsofslopesandchannelsareconsideredlandslidesanddebrisclows,respectively.

IRDR(2014) Thedebrisclowisatypeofslipthatoccurswhenheavyraincausesthedescentofalargeamountofdebris(woods,rocks,mud,etc.)onslopesbytheactionofgravitationalforce.

Hungretal.(2014)

Thedebrisclowisaverydangerousphenomenoninmountainousregions.Thisphenomenonisdifferentfromtheothertypesoflandslidesbecauseofthefactofperiodicoccurrencesthoughtheestablishedtrajectorieswhicharenormallygullyandcirstorsecond-orderbasins.


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conditions (rainfall and water-table). Regardless of origin, such mass movements are commonlycalled landslides.TheUN-InternationalStrategy forDisasterReduction(UNISDR)alsoadoptedthenew classification, since the EM-DAT is the primary database used by the UN, as noted in UNDP(2004).Moreover,asubsequentupdatingoftheclassificationusedbyCREDwasperformed,whichuse no longer the disaster extraterrestrial (GUHA-SAPIR et al., 2012). Thus, Table 2 shows thesummaryofformerandcurrentnaturaldisasters´classificationsestablishedbytheCREDandtheUN.Inthisclassification,thedebrisflowisapartofthe(wet)massmovements,whichindicatesthatthedebrisflowisconsideredonetypeofhydrologicaldisastersbyUN.

Table2.FormerandcurrentratingsofnaturaldisastersinCRED—UN.

Recently,Brazil(2012)launchedtheLaw12608/12establishingtheNationalPolicyofProtectionandCivilDefense(PNPDEC).AsaresultofBrazilianhistory,duetoalotoflossesassociatedwithnaturaldisasters,the PNPDEC shows several aspects, quotes, and intentions that relate to water resources and theirmanagement.AsVenderuscolo&Kobiyama(2007)pointedout,theinterfacesbetweenthePNPDECandtheNationalPolicyofWaterResources (PNRH)whichwasestablishedbyLawNo.9433/97 (BRAZIL,1997)shouldbeanalyzedinmoredetail.

ForabetterexplanationofsomeaspectsofPNPDEC,MinistryofNationalIntegration(2012)publishedtheNormativeInstructionNo.01.InthisInstruction,thereareseveralfragmentsofthetextwherethefederalgovernmentexpressesthewaytoconducttheBrazilianclassificationofnaturaldisasters:

“Art.7ºTheProtectionandCivilDefenseSecretarywilladopttheEM-DAT/CREDclassificationofdisastersandcorrespondentsymbology”.“Art.8ºForattendingtheclassificationofEM-DATtheProtectionandCivilDefenseSecretarystartstoadopttheBrazilianClassificationandCodingofDisasters–COBRADE,asshownonAttachmentIofthisNormativeInstruction.“ATTACHMENTI–BRAZILIANCLASSIFICATIONANDCODINGOFDISASTERS(COBRADE)[…] To suit the Brazilian classification to the classification used by the United Nationsrepresents the follow up of international developments in classification of disasters andrepresentsthelevelingofBraziltotheotherdisastermanagementagenciesallaroundtheworld.FurthermoretheclassificationadoptedbytheUnitedNationsissimplerthanDisastersCoding(CODAR)currentlyusedbySINDEC”.

Fromthethreeexpressionsmentionedabove, it isclearthatthefederalgovernmentintendedtomake the Brazilian classification and coding (COBRADE) very similar to the internationalclassificationusedbytheUN,althoughtheBrazilianclassificationismoredetailed.However,itcanbeclearlyobservedthattheCOBRADEdoesnotfollowthechangeofclassificationperformedbyCRED,andalmostmaintainstheoldstyleclassification(Table3).

As mentioned above, in the international classification, the debris flow corresponds to a type oflandslidesthatfallsintothecategoryofwetmassmovements,whichinturnbelongstothehydrologicaldisasterclass.Ontheotherhand,intheBrazilianClassificationandCodingofDisaster(COBRADE),itbelongs to the category of geological disasters that includes the mass movements that, in turn,encompasslandslides,debrisflows,andsoon.Thesedebrisflowsaredividedintotwotypes:soil/mud


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Formerclassi1ication Currentclassi1ication Maintypes

Geological Geophysical Earthquakes,volcanoes,massmovements(dry)

Meteorological Storms

Hydrometeorological Hydrological Floods,massmovements(wet)

Climatological Extremetemperatures,droughts,cires

Biological Biological Epidemics,pests,insectinfestations


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androck/debriswhosecodesare1.1.3.3.1and1.1.3.3.2inCOBRADE,respectively.Thus,itcanbesaidthattheBrazilianclassificationdoesnotmatchtheinternationalclassificationinrelationtodebrisflows.Sincethisphenomenonisakindofwetmassmovement,debrisflowsshouldbeclassifiedashydrologicaldisastersbyrespectingtheArt.7ofPNPDEC.HereitisworthrememberingthatKobiyamaetal.(2010a)showedthatamongalltypesofnaturaldisasters,hydrologicaldisasters(floods+ landslides)arethoseleadtothemajorproblemsinBrazilandintheworld.

Table3.ComparisonbetweenBrazilianandinternationalclassificationsofnaturaldisasters.

Regardingtothephenomenonitself,tothetypeofflowingmaterial,tothedisastercategoryassociatedwiththisphenomenon,amongothers,thereisawidevarietyoftermsandconcepts.Brunsden(1979)commentedthattheterminologyandclassificationofdebrisflowsarenotsatisfactory.Aliteraturereviewconductedbythepresentstudyshowsthatthisproblemstillremainsinthescientificcommunity.Addingtothecomplexityanddifficultyinidentifyingthephenomena,theabsenceofadministrativeagreementmakestheinvestigationsurveyinaliteraturemorecostlyandcomplicated.

Basedonalltheaboveexamples,thepresentstudyusesthetechnicalterm"debrisflow"anddefinesit as a flowing phenomenon that occurs from the landslide initiation. Due to the fluidity of themixture,itsrunoutisoftenverylong.However,thepresentstudydoesnotdiscussindetailthisvalue.

3.Materialsandmethods

ConsideringthediversityofPortugueseterms(Zluxodedetritos,Zluxosdeescombros,corridasdemassa,escorregamentos,deslizamento,etc.), thepresentstudysearchedthedatabasesavailableon the Internet and in libraries, undergraduate´s monographs, master´s theses, and doctor´sdissertationsproducedinBrazilianuniversities.Bytryingtocollectthelargestpossiblenumberof papers dealingwith debris clows in Portuguese and English, papers published in scienticicmeetingsandjournalsaswellasinternationalandnationalbooksinthecieldofgeosciencesandengineeringweresought.

Theinformationcontainedineachpaper(forexample,thephenomenondescriptionandphotos)wasalsousedtojudgewhethertheworkingtopicwasreallyrelatedtodebrisclow.Forexample,

BrazilianClassi1ication(COBRADE) InternationalClassi1ication

Class Example Class Example

Geological

• Earthquakes• Volcanism• MassMovements• Erosion

Geophysical• Earthquake• Volcanism• MassMovements(dry)

Meteorological • Large-scalesystems• Storms• Extremetemperatures

Meteorological • Storms

Hydrological • Floods• Flashcloods• Waterloggings

Hydrological • Floods• Massmovements(wet)

Climatological• Drought Climatological

• Extremetemperatures• Dry/drought• Fires

Biologic • Epidemics• Infestations/pests Biologic

• Epidemics• Insectinfestations• Stampedesofanimals


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if one paper addressed only translational landslides, it was not considered as a publicationrelatedtodebrisclows,andwasexcludedfromthecinalanalysisinthepresentstudy.

4.Resultsanddiscussion

4.1.Oldrecord

Schlumberger(1882,citedTAKAHASHI,1983)wroteoneofthefirstreportsaboutdebrisflowsintheworldliterature.SeekingfortheoldBrazilianliterature,anaccountofthepriestAnchietadescribinghisexperienceinPiratininga,SãoPaulostate,in1560wasfound(CORRÊAFILHO,1954):

[…] It fell so violently that seemed to threaten us with the Lord destruction; shook thehouse,snatchedtheroofsandoverthrewthewoods;thecolossaltalltreesrippedupbytheroots,brokeintoothersmallerpieces,smashedother,sothattheroadswereblocked,andtherewasnopassagethroughthewoods, itwastowonderhowmanydamagetreesandhousesproducedinhalfanhour.[…](CORRÊAFILHO,1954).

It isnotedthatthisreportprobablydescribestheoccurrenceofanextremely-intensiverainfalleventanda seriesofdebris clows (ormud clow).Therefore, this canbe considered theoldestrecordrelatedtothisphenomenoninBrazil.Afterhim,severalpeoplerecordeddebrisclowsinmoreorlessscienticicways.

4.2.Historicalanalysis

InthesurveyconductedbysearchingtheInternetandinlibraries,162workspublishedduringtheperiod1949-2014weretotallyfound.ThedetaildescriptionofallthepublicationsisinKobiyama&Michel(2015).Althoughtheresearchedperiodextendsfromthebeginningofthetwentiethcentury,no technical-scientific report was elaborated by 1949. It was noted that many Brazilian works,directlyorindirectly,adoptedaclassificationofVarnes(1978).Figure1showsthenumberofworksdivided into four categories: books; papers in journals; papers in proceedings; and monographs(theses,dissertationsandtechnicalreports).Mostofpublicationsarepapersinproceedings,whichimplies a limited quality of scientific production related to this phenomenon in Brazil. The smallnumberofscientificbookshascausedthedifficultyinherenttothestudyofthisphenomenon.

Figure 2 shows the historical trend of scientific studies during the period from 1900 to 2014.Althoughvariouspublicationshavebeenmadeintheperiod1966-1975,inthe1990sasignificantincreaseinpublicationsbegan.


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26

98

29

9

Book & Book chapterPapers in JournalsPapers in ProceedingsMonographs

Figure1.istributionofpublicationsofscienticicpapersondebrisclowinBrazilduringthe1900-2014period.


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Figure2.ThescienticicworkhistoryondebrisclowsinBrazilinthe1900-2014period.

AnalyzingMarcelinoetal.(2006)andTominagaetal.(2009),amongothers,thepresentstudysoughtinformationonoccurrencesofdebrisflowsinBrazilduringtheperiod1900-2014.ItcanbesaidthattheoldestdisastercausedbydebrisflowinBrazil,technicallyregistered,tookplaceinSantosin1928,causing 80 deaths and partial destruction of the Santa Casa hospital. Nevertheless, the scientificcommunity did not investigate this disaster. Table 4 shows that during the period 1966-1975disastersrelatedtolargedebrisflowoccurred.Inaddition,fromthe1990s,debrisflowsthatcausedlargenumbersoffatalitiesoccurredmoreoften.AcomparisonofFigure2withTable4confirmsthatthenumberofpublicationshasbeenelevatedwiththeincreaseoftheoccurrenceofdebrisflows.

Table4.DisasterwithdebrisclowsinBrazil(1900-2014).

Year Location Numberofdeaths(approximate)

1928 Santos(SP) 80

1948 ValedoParaíba(SP/RJ) 250

1956 Santos(SP) 64

1966 RiodeJaneiro(RJ) 100

1967 SerradasAraras(RJ) 1700

1967 Caraguatatuba(SP) 120

1971 Salvador(BA) 104

1972 CamposdoJordão(SP) 10

1974 Tubarão(SC) 40

1986 Lavrinhas(SP) 11

1988 Cubatão(SP) 10

1988 Petrópolis(RJ) 171

1988 RiodeJaneiro(RJ) 30


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14

18

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1945

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1975

1980

1985

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ModicicationfromMarcelino(2003)andRosaFilho&Cortez(2008).

4.3.SuggestionsfornecessaryactionsinBrazil

ThehistoricalanalysisofstudiesondebrisflowsinBrazildemonstratesthecurrentsituationandbrings several actions that should be urgently implemented. Based on the fact that studies ondebris flows may be relevant in understanding the mechanism of sediment production andmanagement of debris-flow disasters, the present study suggests (1) establishment of standardconceptandterminology;(2)systematizationofhydro-meteorologicalmonitoringandtopographysurveying;(3)registrationoftheoccurrencesanddatabaseconstruction;and(4)developmentofresearchonwoodydebrisflows.

4.3.1.Establishmentofstandardconceptandterminology

Asabovementioned,peopleinBrazilusethevarioustermsfordebrisflows,forexamples,fluxodedetrito,fluxodeescombros,corridademassa,andsoon.ThoughtheProtectionandCivilDefenseinBraziluses the termcorridademassa in theCOBRADE, this termdoesnot seempopular in thescientific community. Furthermore, in terms of disaster, this phenomenon is classified ashydrologicalbyCRED(international)andasgeologicalbyCOBRADE(nationallevel).Thus,existsadivergenceinterminologyandconceptrelatedtothisphenomenon.

Sincedebrisflowshaveatransitionalandfluiditycharacteristics,subjectivityliesonitsdefinition,identificationanddescriptioneven in thescientific community.Toreduce thesubjectivity in theidentification of these phenomena, some criterions could be used. For example, Wilford et al.(2004) considered the debris flow, debris flood and flood as hydrogeomorphic processes andproposedaquantitativemethodtodifferentiatethembymorphometry.This typeofquantitativemethodologyshouldbeincreasinglysoughtandusedinBrazilinordertoimprovetheregistrationmethodology.SincetheenvironmentinBrazilischaracterizedwithhightemperature,rainfallandbiodiversity,debrisflowsinBrazilmaydifferfromthoseoutsideofBrazil,especiallyinEuropeandNorthAmerica. TheBrazilian scientific community should, hence, discussmore to establish thestandardterminologyandconcept.

4.3.2.Systematizationofhydro-meteorologicalmonitoringandtopographysurveying

It is commonly said thatheavy rainfalls can causedebris flows (ZNAMENSKY,2014).Therefore, therainfallnecessarytotriggerdebrisflows(forexample,SUZUKIetal.,1979;SUZUKI&KOBASHI,1981;SUZUKI&KOBASHI,1987;GLADE&WIECZOREK,2005)andlandslides(e.g.,TATIZANAetal.,1987;MICHELetal.,2015)isoneofthemainissuescurrentlyaddressedinscienceandtechnologydedicatedtodisastermanagement.Debris flowsalmostalwaysoccurwithheavyrainfalls.Due to this fact, theCREDreviseditsclassificationofnaturaldisasters,insertingdebrisflowsinthecategoryofhydrologicaldisasters.Sohydrologicalmonitoring,especiallyofrain,shouldbeevenmoreintensifiedinBrazil.

1989 Salvador(BA) 100

1990 Blumenau(SC) 14

1992 Contagem(MG) 36

1995 TimbédoSul(SC) 29


2008 ValedoItajaí(SC) 135

2010 AnguladosReis(RJ) 30

2011 SerraFluminense(RJ) 978



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Toadvancefurther,itisnecessarytoimplementanautomaticmonitoringsystemofrainfallanddischarge. Since debris clows are phenomena that occur abruptly, especially in mountainousregions, this system should be implementedmore intensively in the headwaters regions andpreferablyshouldhavehightemporalintensivedatacollection(measurementintervalsequalto10minutesorshorter).

Thesedimentproductionassociatedwithadebriscloweventistypicallyhigh,whichcanclearlybeobservedinthecield.However,recognitionofamorequantitativeperspectiveofeventsisstillfarfromsatisfactorycondition.Itisduetothelackoftopographicalinformationbeforeandaftertheevent.Then,thesteeperregionswhichexhibitagreatertendencytotheoccurrenceofdebrisclows should be topographically described with greater precision and frequency. In addition,conductingsurveys in the initiationzones, transportanddepositionofnewlyoccurringdebrisclowscanprovideimportantinformationinadvanceofstudiesthataddressthephenomenon.

4.3.3.Registrationoftheoccurrencesanddatabaseconstruction

A science or a scientific study of one phenomenon almost always starts from its observations.Therefore, toadvance thescienceofdebris flows, therecordofall the instances, regardlessof theeventthathavecausedadisaster,isfundamental.Thereareseveralequationsestablishedonlyfromdatabaseswhich containedoccurrences records, forexample, theequation that relates the runoutangletothetotalvolumeofproducedsediments(COROMINAS,1996;RICKENMANN,1999).SinceanequationthatdescribestheBraziliansituationhadnotyetbeenelaborated,Kobiyamaetal.(2010b)compared their resultswithphenomena thatoccurred inEurope,usingone figureofRickenmann(2005).ToverifythesimilaritybetweenBrazilianandEuropeansituationsandtogenerateitsownequationdescribingBraziliandebris flows, it is imperative that a database containingdebris flowoccurrencesrecordsiscreatedandfullyavailabletoallinterestedsectors.

In the preparation of records and database construction, it is necessary that certainminimumstandardsarehighlighted.Thereare, ingeneral,suggestionsandmanuals for landslidesrecords,forexample,handbookorguidanceofHighland&Bobrowsky(2008)andCorominasetal.(2014).However,adetailedmanualtorecordtheoccurrenceofdebrisflowhasnotelaboratedyet.Rainfallregime, topographic information and occurrence time are the fundamental characteristics to berecorded.Furthermore,ifpossible,pedological,geological,sedimentological,rheological,hydraulic,andotherhydrologicalcharacteristicsshouldbealsoregistered.

4.3.4.Developmentofresearchonwoodydebris1lows

Normally,debrisflowshaveamixtureoftwophases(waterandsediment).Inthecaseofamountainousregioncoveredbyforest,thetrunksrepresenttheirsignificantpresence.However,theeffectsoftrunks(orvegetationingeneral)ontheoccurrencemechanismsofdebrisflowsarenotrecognizedscientificallyinasatisfactoryway(LANCASTERetal.2003;STOFFEL&WILFORD,2013).Althoughthereareseveralattemptstomodelthewoodydynamics intheflows(WALLERSTEIN,2003;MAZZORANAetal.,2011;SHRESTHAetal.,2012),nomodelisstillcapabletodoitverysatisfactorily.

For the temperate climate condition, Seo et al. (2010) conducted a literature review on thedynamicsofthelogsattheriverbasinlevel.Theirdescriptionwasjustqualitative.InBrazilthetropical and subtropical climates facilitate the increase both in the biodiversity and in thebiomassinthebasins,especiallyinriparianzones.Sincetheriparianvegetationisveryrich,thepresenceofvegetationandlogscanbeexceptionallysignicicantforthedebrisclowoccurrences.Itmeansthat,whenadebrisclowoccursinBrazil,itcanbecategorizedasawoodydebrisclow.Thus,studiesinBrazilshouldfocusonthedynamicsofthelogsinthefullcontextofdebrisclow.

5.Finalconsiderations

DebrisflowsdonotoccurfrequentlyinBrazil.However,whentheyoccur,theyarecapabletocauselargelossesandfatalities.Inordertoreducedisastersassociatedwithdebrisflows,severalmeasures


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arerequired.Amongthem,theregistrationanddescriptionofsuchphenomenonatthemomentoftheir occurrence as well as education/training prior to its occurrence should be emphasized. Topromoteeducationrelatedtodebrisflows,teachingmaterialswhichinturndependontheexistenceof records are indispensable. Because such phenomena usually occur in mountainous regions,ordinary citizens need to receive a good education on this topic for registering them moreappropriate and detail. Goerl et al. (2012) reported that the debris flowmay be one of themainobjectsofhydrogeomorphicstudy.Hence,thisscienceshouldbemorewidespreadatalllevelsofeducationinBrazilandshouldadvancetheunderstandingofthisphenomenon.

Duetothehighspeedandhugeextension,thedebrisflowisconsideredanimportantgeomorphicagent.Itsoccurrencecanbeasourceoflargeamountsofsedimenttotherivernetwork(GABET&DUNNE,2003).AccordingBendaetal.(2003),thedebrisflowchangesthefluvialmorphologyandaffects aquatic ecology. Along the large period, this phenomenon significantly contributes to thesedimentsproductionandconsequentlythelandscapeevolutionofsteepbasins(STOCK&DIETRICH,2003).Therefore,fromatechnicalpointofview(disastermanagement,soilandwaterconservation,etc.)andfromascientificpointofview(hydrology,geomorphology,andhydrogeomorphology),itisstronglyrequiredtoincreasethenumberofstudiesandpublicationsrelatedtodebrisflowsinordertopopularizeandeducatethisphenomenoninthecommunity.

5.1.Acknowledgements

The authors thank themembers of the Research Group on Natural Disasters (GPDEN) of theInstituteofHydraulicResearch(IPH)oftheFederalUniversityofRioGrandedoSul(UFRGS)fordaily discussion of debris clow and also Brazilian National Council of Research (CNPq) forprovidingscholarships.

6.References

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