Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 ·...
Transcript of Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 ·...
![Page 2: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/2.jpg)
Costsandbenefitsoffloods• Costs:damagetoinfrastructureandhouses,lostlivesandcrops• Benefits:sedimentation providesfertilelands,flushingofstagnantwaterandpollutantsandopportunitiesforfloodbasedfarming
Goal:toadapttotheconstrainsthatfloodsimposeandtakeadvantageoftheirbenefits
![Page 3: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/3.jpg)
Interactionsbetweenroadsandfloods•Roadsfragmenthabitatsandinterrupttheflowofwater,sediments,nutrientsandaquaticlife
• Roadscanactforinstanceas‘reservoirdam’tokeepwaterforirrigationinthedryseason
• Floodscausedamagetoinfrastructureincreasingmaintenancecosts
• Floodingononesideoftheroadanddryingoutontheother,alteringvegetationandassociatedspecies
![Page 4: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/4.jpg)
RoadsinfloodplainsConstruction-Maintenance Drainage characteristics Erosion susceptibility Water Harvesting potential
Elevatedsubgradesandembankmentscanincreasecostsasconstructionmaterialinfloodplainscanbescarce.
Laminarflowsthroughfloodplainsrequirewidedrainagesystems,floodcontrolmechanismssuchasflapgatesorsurfacedrainageoutlets.
Waterloggingonbufferareasbetweenroadembankmentsandfloodplain.
Floodinterception– lessmoisture(sediments)ondownstreamareas.Thiscanhavemajorimpactonfloodplainagriculture
Shallowgroundwater–handdugwellsandmanualdrilledboreholesaswellasdugoutpondsandborrowpits
![Page 5: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/5.jpg)
Roadsasfloodcontrolmechanisms• Roadssubgradesandembankmentsactasdikes,manyroadsintheNetherlandsarelaidonthetopofdikes.
• Inareaspronetoperiodicalfloods– roadsmayserveasfloodregulators.
• Roadslaidinfloodplainsoftenblockfloodflowfrontsdiminishingfloodareas.
• Thisscenariocouldberevertedifroaddesignprinciplesaremodified.
• Roadmaybeopentofloodflowsenabling“floodcorridors”includingbridgesandlongculverts,flapgatesandfusingsluicegates.
• Thusroadscanactasfloodregulators,controllingfloodanddrainagepatterns.
![Page 6: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/6.jpg)
Roaddesigninfloodplains• Planninganddesignshouldtakeintoaccountthelocalfloodflowpatterns• Assesstheexistinghydraulicbehaviourofdrainagepaths,waterwaysandfloodplains,withparticularreferencetoknownandpotentialfloodlevelsinthevicinityoftheroadalternatives.• Identifyandassessthepotentialshort- andlong-termimpactsofconstructionandoperationonthequantityandqualityofsurfacerunoff,floodplaininundationandwaterwaywaterquality.
Damagetoruralroadbyflood
![Page 7: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/7.jpg)
Importantquestionstobeaddressedduringplanningphase•Willtheprojectaffectanexistingwatercourseorfloodplain?
•Willtheprojectchangeeithertheroaddrainageornaturallanddrainagecatchments?
•Willtheprojectchangethenumberortypeofjunctions?
•Willearthworksresultinsedimentbeingcarriedtowatercourses?
•Willtheprojectallowdrainagedischargestotheground?
![Page 8: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/8.jpg)
Roadembankmentgeometry•TherecommendedcrestlevelforNationalandProvincialroadsisthehighestrecordedfloodlevelplus0.5meters.Forregionalroadsthecrestlevelshouldcorrespondwithaminimumheightofthewaterleveloffloodswitharecurrenceof10yearsplus0.25meters.
• Forroadembankmentsupto4metershighaslopegradientof1:3providessufficientsafetyprotectionagainstthemacro-instabilitymechanismduringtheriseandfallofthewaterlevel.
•Investigatethegeotechnicalcharacteristicsofthetopsoilsandtakeadequatemeasuresinroaddesign,forexampleremovalofinappropriatetopsoils.
![Page 9: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/9.jpg)
Resistancevsresiliencestrategies• Resistancestrategy:embankmentsandroadsareconstructedtoprotectrextractareasfromtheinfluenceoffloods
• Disadvantages:o pressureonthestructurecancausedamageandhighmaintenancecosts
o floodplainhydraulicsaredisrupted,whichnegativelyimpactsonthefloodplainecosystem
o waterqualityproblemsbecausedirtandpollutedwaterarenolongerremovedbythefloodwaters
![Page 10: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/10.jpg)
Resistancevsresiliencestrategies• Resiliencestrategy:minimizingtheconsequencesoffloods,butatthesamemaintainthenaturalfloodplaindynamicsasmuchaspossible.
•Mightrequirehigherinitialinvestment,butlongertermcostsintermsofroaddamageandecologicalimpactswillbelower.
• Importanttolocatebridgesandculvertsatthebestpossiblelocationsandrecommendsolutionsthathaveonlysmalladditionalconstructioncosts.
![Page 11: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/11.jpg)
Waterspreadingweirs• Exampleofresiliencestrategy
• Temporaryfloodsareroutedoutofthedryriverbedssoastoinundatethesurroundingarea
• Therivercrossingsaswellasembankedroadsleadingtothemactasfloodspreaders
• Dropstructuresandcrossdrainageisprovidedsoastoensuretheirstability
![Page 12: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/12.jpg)
Exampleofresilienceapproach:RoomfortheRiverintheNetherlands• Createssafetyagainstextremeriverfloodsbywideningrivercrosssectionstolowerfloodlevels.
• Situatingthedikesfurtherawayfromtheriver,orloweringtheriverforelands,toreducevelocitiesandwaterlevelsbyprovidingspaceforthewatercourse.
•Requiresproperlydesignedflow-throughstructuresthatcanwithstandthehighflowvelocities.
![Page 13: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/13.jpg)
Approach Pros Cons
Resistancestrategy • Betterprotectionagainstfloods• Reductiondamageinhighdensity• areas
• Fragmentationoffloodplainsandhydraulicchangesandimpactonflood-relatedfunctions
• Downstreamimpacts• Moreexpensivetoprotectroads
againstdamage
Resiliencestrategy • Lessfragmentationfloodplainsandhydraulicchanges
• Lessdamagetoroads• Long-termbenefitstoboth
financialinvestmentindevelopmentandbiodiversityconservation
• Increasedawarenessofdangersoffloodplainliving
• Morecostlyduetoconstructionthrough-flowstructures
• Reducedaccess(lowerroads)• Moreneedforintegratedplanning
andmanagement
![Page 14: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/14.jpg)
Integratedapproach• Floodmitigationmeasuresupstreamsuchasprotectiondikes,drainagefromprotectedareas(irrigationschemes,cities,towns)orflushingoffloodwaterfromreservoirswillaffect floodconditionsdownstream.
• Land-usedevelopmentandconstructionofroadsandthrough-flowstructureschangethenaturalfloodflowpatternsandincreasefloodriskstoadjacentareasaswell.
![Page 15: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/15.jpg)
Conclusions• Roaddevelopmentsinafloodplainsystem,requireadifferentapproachtoplanningandtechnicaldesign,comparedtoroaddevelopmentsinareasthatarenot(regularly)inundated
• Needforharmonisationofstandardsandguidelinesandinclusionofthespecificsofdevelopingroadsinadynamicfloodplainsystem
• Searchforawin-winsolutionwhererobusttechnicaldesignsleadtobenefitsforvariousconstructioncost,infrastructuremaintenance,ecology,naturalresourcesandvulnerabilityofpopulation.
![Page 16: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/16.jpg)
Designrecommendations1. Tailoralignmentanddesignsolutionstothespecificfloodplainhydraulicand
ecologicalsituation
2. Thenumberanddimensionsofflowthroughopenings(bridgesandculverts)shouldbesuchthatinterferencewiththenaturalhydraulicsofthefloodplainintermsofextentanddurationisminimal
3. Scourprotectionnearbridgesandotherflow-through openingsinordertopreventdamagetotheabutmentsandeventuallythestructureitself
![Page 17: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/17.jpg)
Recommendationsfortechnicaldesignguidelines1. Updateandreviewthedesignstandardsandguidelinessoroaddesigners
havebetterguidanceandbest-practiceexamplesofhowtodevelopfloodproofedandenvironmentallyfriendlyroads
2. Incorporateahydraulicanalysisordeterminationofthefloodhydraulicsandloadsonroadstructures
3. Makecostsanalysisforthedifferentoptionsofslopeprotection,costsofflowthroughstructures(bridgesandculvertsetc)andquantifytheoptionsintheintegratedapproach
![Page 18: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/18.jpg)
Researchandcapacitybuilding• Improveknowledgeofthefloodplainsystemintermsofinteractionsbetweenfloodplainhydraulicsandbasindevelopments,functionsofthesystem,criticalthresholdstomaintainthesefunctionsandvaluesofthefunctions.
• Investineducation,trainingandtechnicalsupporttointroduceand/orstrengthenpracticeofintegratedplanningofroaddevelopmentandrehabilitation.
![Page 19: Roads in floodplainsspate-irrigation.org/wp-content/uploads/2017/11/Roads-in... · 2018-01-22 · Roads as flood control mechanisms •Roads subgrades and embankments act as dikes,](https://reader033.fdocuments.us/reader033/viewer/2022041905/5e63065412a0200f242d25a8/html5/thumbnails/19.jpg)
Generalrecommendations• Applyanintegratedplanningapproachthatconsiderstheconsequencesofthedevelopmentthroughoutthesystemincludingenvironmentalandsocialimpacts.
• Applyafloodplainsystem’sapproachinwhichnotonlylocalimpactsofroadsbutalsoregionalandcumulativeimpactsareconsidered.
• Providesufficientcoordinationbetweenroaddevelopmentandrehabilitationplanningandothersectorplanning.
• Assesspossibletransboundary (provincial,national,international)impactsofroaddevelopmentandrehabilitation