Testing The Validity Of Hydraulic Losses Described In The CIRIA Methodology For Culvert Design

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School of Civil Engineering
Faculty of Engineering
CIVE5708M
Individual Research Project Dissertation
Submitted in partial fulfilment of the requirements for the degree of
Master of Engineering (Civil and Structural Engineering)
Testing the Validity of Hydraulic Losses
Described in the CIRIA Guidance
Methodology for Culvert Design
by
Chiko Tembo
August 2016

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Abstract
Hydraulicmodellingis ameansthroughwhich hydrologicpractitionerscarryoutan assessment
of waterlevelsforagiventestreach.Sucha practise if oftenmetwithdifficultyindischarge and
waterflowlevel measurement particularlyduringfloodevents.Undersuchconditions,the
developmentof ratingcurvesisoftensoughtinorderto estimate discharge patternsinriversand
watercourses.
The followingstudywascarriedoutinorderto testthe validityof hydrauliclossesdescribed
withinthe CIRIA methodology.The hypothesisisthatfornon-standardculverts,the CIRIA tendsto
overestimateheadlosses whichinturn,leadstoincreasedupstream waterlevels.Hitherto,studies
on thissubjectareahave not beencarried outand there appearstobe an impendingneedto
address the matterof headlossoverestimationsof the CIRIA particularlywhere culvertmodellingis
concerned.
The research involved modellingatestreach fora mostrecentfloodeventthattookplace in
withinNorthernEnglandduringthe 2015 festive period.The model wasdevelopedonthe software
FloodmodellerProand model characterisesof the testsite suchas culvertgeometryandentrance
losscoefficients calibrated intothe model.These inputswhereextracted fromThe CIRIA
methodology aswell asHydraulicDesignManual –TexasDepartmentof Transportationandwere
compared againsteachother inorderto gauge performance andverifythe hypothesis.Itwasfound
that the CIRIA methodologydoesnot leadtooverestimates butinfact,outperforms the inlet
coefficientsdescribedwithinthe HydraulicDesignManual.The resultsfrom thisresearchare enough
to encourage the use of the CIRIA methodologyoverthe HydraulicDesignManual methodologyfor
hydraulicmodellingpurposes.

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Acknowledgements
Foremost,Iwouldlike toexpressmygratitude to mysupervisorSimonJeppsforhissupervisionover
my research. Thisthesiswouldnothave beenpossiblewithouthisconstructivecriticism, professional
guidance andimmense knowledge inthe fieldof HydraulicModelling.
My sincere thanks goes to the University of Leeds for providing me with the excellent facilitiesand
supportthat aidedinthe completionof thisthesis.
My heartfeltgratitude goestomyfamilythatcontinuestosupportme andmyideaseverystepof the
way. I am grateful for my parents for giving me birth and a grand opportunity to study abroad in
Englandinsuchanoutstandingandreputableuniversity. Iwouldalsoliketothankmysisters Thokozile
and Towelafor beingsupportive. Mylove foryou both isunfailingandjust.
I would like to also express my deepest appreciation to my friends for their support, patience and
givingme the platformtorantaboutmychallengesandlife’scomplexitiesonthisjourneyof university
and job applications: Paul Philips, Nathaniel Dixon, Steven Taylor, Jake Perkins, David Broome and
Giedre Bliudziute.
Kindestregardstothe AnytimeFitnesssquad,toomanytomentionbynameforyourencouragements.

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Table of Contents
Abstract.......................................................................................................................................2
Acknowledgements ...................................................................................................................... 3
List of Tables and Figures .............................................................................................................. 6
1 Introduction.......................................................................................................................... 8
1.1 Overview....................................................................................................................... 8
1.1.1 Aims and Objectives ............................................................................................... 9
2 Background Review............................................................................................................. 11
2.1 Relationship between Manning’s and Rating Curves ...................................................... 11
2.1.1 Section Control..................................................................................................... 13
2.1.2 Channel Control.................................................................................................... 14
2.2 Factors to Contest with When Interpreting the Stage-Discharge Relationship.................. 15
2.3 Particular Circumstances that Affect Rating Curves Sensitivity........................................ 16
2.3.1 Ice Covered Rivers................................................................................................ 16
2.3.2 Coastal Rivers....................................................................................................... 16
2.3.3 Theoretical Computations..................................................................................... 16
2.4 Culvert Design ............................................................................................................. 17
2.4.1 Inlet Control......................................................................................................... 17
2.4.2 Outlet Control...................................................................................................... 17
2.5 Energy Dissipation ....................................................................................................... 19
2.5.1 Conventional Systems........................................................................................... 19
2.6 Improved Systems for Culvert Inlet and Outlet .............................................................. 20
2.6.1 Bevel-edged Inlets................................................................................................ 20
2.6.2 Side–Tapered Inlet................................................................................................ 21
2.6.3 Slope-Tapered Inlet.............................................................................................. 22
2.7 Culvert Wing Walls....................................................................................................... 22
2.8 Culvert Outlet.............................................................................................................. 24
2.8.1 Culvert Outlet Energy Loss .................................................................................... 24
2.9 Effects of Culvert Barrel Number .................................................................................. 24
2.10 Culvert Rating Curve .................................................................................................... 25
2.11 Materials..................................................................................................................... 26
2.12 Culvert Positioning....................................................................................................... 26
2.13 Hydrographs................................................................................................................ 28
2.13.1 Storm Hydrographs............................................................................................... 28
2.13.2 Interpretation of Storm Hydrographs..................................................................... 29

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2.14 Factors Affecting Storm Hydrographs............................................................................ 29
2.14.1 Area and Channel Slope........................................................................................ 29
2.14.2 Geotechnical Characteristics ................................................................................. 30
2.14.3 Environment........................................................................................................ 30
2.14.4 Precipitation and Temperature.............................................................................. 30
2.14.5 Land usage........................................................................................................... 30
2.15 CIRIA Guidance and Hydraulic Design Manual – Texas Department of Transportation...... 30
2.15.1 Flood Simulation Software .................................................................................... 31
3 Research Gap...................................................................................................................... 34
4 Research Methodology........................................................................................................ 35
4.1 Introduction................................................................................................................ 35
4.2 Instruments................................................................................................................. 35
4.3 Research Design.......................................................................................................... 35
4.3.1 Stage 1................................................................................................................. 35
4.3.2 Stage 2................................................................................................................. 37
4.3.3 Stage 3................................................................................................................. 38
4.4 Data Analysis............................................................................................................... 38
4.5 Limitations .................................................................................................................. 39
5 Results................................................................................................................................ 40
5.1 Stage 1........................................................................................................................ 40
5.2 Stage 2........................................................................................................................ 43
5.3 Stage 3........................................................................................................................ 46
6 Discussion........................................................................................................................... 57
7 Conclusion.......................................................................................................................... 61
8 References.......................................................................................................................... 62
9 Appendices......................................................................................................................... 66
9.1 Appendix A – User forum............................................................................................. 66
9.2 Appendix B – Video recording....................................................................................... 67
9.3 Appendix C – Upstream and Downstream CVP gauge levels............................................ 68

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List of TablesandFigures
Figure 1-1 Annual numberof worldwidenatural disastersbetween1900 and 2006 (Source:Junichi
and Yoshitani, 2009) ..................................................................................................................... 8
Figure 2-1 Likelihood calculation of rating-curves......................................................................... 12
Figure 2-2 Section control (Source: Braca, 2008)........................................................................... 14
Figure 4-1 Locationof Burnleyroadculvertonthe riverCalder,Todmorden(Source:Google maps,
2016) ......................................................................................................................................... 36
Figure 4-2 Upstream culvertjunction to Central Vale park reservoir (Source: Tembo, 2016) ............ 37
Figure 5-1 12 November Upstream and Downstream level series.................................................. 40
Figure 5-2 12 November time-steps............................................................................................. 40
Figure 5-3 12 December Upstream and Downstream level series................................................... 41
Figure 5-4 12 December time-steps............................................................................................. 41
Figure 5-5 Boxing Day Upstream and Downstream level series...................................................... 42
Figure 5-6 Boxing Day time-steps................................................................................................. 42
Figure 5-7 Boxing Day High Manning rating curve scenario (Source: Tembo, 2016) ......................... 43
Figure 5-8 Boxing Day Low Manning rating curve scenario (Source: Tembo, 2016).......................... 44
Figure 5-9 Boxing Day Best Manning rating curve scenario (Source: Tembo, 2016) ......................... 44
Figure 5-10 High Manning rating curve scenario for combinedflood events (Source: Tembo, 2016) 45
Figure 5-11 Low Manning rating curve scenario for combined flood events (Source: Tembo, 2016) . 45
Figure 5-12 Best Manning rating curve scenario for combined floodevents(Source: Tembo, 2016). 46
Figure 5-13 Boxing Day stage series (all combinations).................................................................. 47
Figure 5-14 12 November stage series (all combinations).............................................................. 47
Figure 5-15 12 December stage series(all combinations).............................................................. 48
Figure 5-16 Coping stone height.................................................................................................. 49
Figure 5-17 Best CIRIA target variations for all events................................................................... 53
Figure 5-18 High CIRIA target variations for all events................................................................... 53
Figure 5-19 Low CIRIA target variations for all events.................................................................... 54
Figure 5-20 Best Non-CIRIA target variations for all events............................................................ 54
Figure 5-21 High Non-CIRIA target variationsfor all events............................................................ 55
Figure 5-22 Low Non-CIRIA target variations for all events ............................................................ 55
Figure 5-23 No Loss target variations for all events....................................................................... 56
Figure 6-1 Boxing Day Flow series for CIRIA instance..................................................................... 58
Figure 6-2 Boxing Day Flow series for Non-CIRIA instance ............................................................. 58
Figure 6-3 12 November Flow series for CIRIA instance................................................................. 59
Figure 6-4 12 November Flow series for Non-CIRIA instance.......................................................... 59
Figure 6-5 12 December Flow seriesfor CIRIA instance ................................................................. 60
Figure 6-6 12 December Flow seriesfor Non-CIRIA instance.......................................................... 60

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Table 1-1 Frequencyof natural disastersbetween1900 and 2006 (Source:Junichi andYoshitani,
2009) ...........................................................................................................................................8
Table 2-1 Main factors affecting Inlet and Outlet control (Source: FishXing, 2006).......................... 19
Table 2-2 Sources of uncertainty ................................................................................................. 33
Table 4-1 Manning'ssurface roughnessandentrance losscoefficientcombinationsmatrix(Source:
Tembo, 2016) ............................................................................................................................. 39
Table 5-1 Surface roughness coefficients extracted from Chow (Source: Chow, 1959) .................... 43
Table 5-2 Culvertinletgeometricdescriptionandcorrespondingentrance losscoefficients(Source:
Flood Modeller Pro, 2016; Garcia, 2016) ...................................................................................... 46
Table 5-3 12 November modelled CVP levels................................................................................ 50
Table 5-4 12 December modelled CVP levels................................................................................ 50
Table 5-5 Boxing Day modelled CVP levels.................................................................................... 51
Table 5-6 12 November modelled CVP levels expressed in mm difference...................................... 51
Table 5-7 12 December modelled CVP levels expressedin mm difference...................................... 52
Table 5-8 Boxing Day modelled CVP levels expressed in mm difference ......................................... 52
Table 6-1 Top performing rating curves........................................................................................ 57

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1 Introduction
1.1 Overview
The UnitedNationsEducational ScientificandCultural Organisation(UNESCO) reportsonthe global
trendson water-relateddisastersandhaslistedflooding asthe numberone fatal natural disaster
(Junichi andYoshitani,2009).It is furtherstatedthatoverthe past century,the frequencyof floods
has increasedworldwideascomparedtootherwater-relatedandnon-waterrelateddisasters.
Figure 1-1 and Table 1-1 belowdepictthesestatistics.Aswithall natural disasters,there are many
associatedsocial,economicandenvironmental consequences,particularlyinrelationtolossof
humanlife andlivestock,destructionof infrastructure,environmentaldegradationandeconomic
recoverycosts.
Figure 1-1 Annual number of worldwide natural disasters between 1900 and 2006 (Source: Junichi and Yoshitani, 2009)
Table 1-1 Frequency of natural disasters between 1900 and 2006 (Source: Junichi and Yoshitani, 2009)

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The EuropeanEnvironmentagencyreportedthatbetweenthe periodof 1998 and 2009, flooding
eventsaccountedfor1,126 fatalitiesandover60 billionEuroswere incurredindamages.These
losseswere attributedtothe increase inpopulation,particularlyinthe areassusceptible toflooding
(EEA,2010, citedinKauffeldtetal.,2015).
Duringthe winterof December2015 to January2016, the north of England,Wales,Scotlandand
NorthernIreland,experiencedsevere storms(Desmond,EvaandFrank),whichlastedthroughthe
festive season,andresultedinsevere floods.There have beenconfirmedreportsthatthe floods
causedby StormDesmondinCumbriaandLancaster resultedinthe floodingof 5,200 homesand
causedone fatalityinCumbriaandanotherinNorthernIreland(BBCNews,2015). The economic
impactof StormDesmondisexpectedtobe overhalf a billionpoundswithinsurancecompanies
incuringcostsbetween£250 - £325 million(Priestley,2016).
The trail of destructionleftbehindbyStormEvaresultedindestructionof 9,000 propertiesanda
total of 16,000 fromthe combinedstorms,DesmondandEva.The effectsof StormEva were
concentratedaroundWestYorkshire andLancashire,withsevere floodinginLeeds,YorkandGreater
Manchester,duringDecemberBoxingday2015 (Priestley,2016). StormFrank wasconcentrated
mostlyinthe westernpartsof the UnitedKingdomandNorthScotland.Strongwindsandrainfall
overa 24 hourperiodleft13,000 homeswithoutpower(Becton,2015).
In orderto successfullyandeffectivelymitigatethe impactof flooding,itisimportantforincumbent
hydrologiststohave some reasonableknowledge aboutdisasterriskmanagementand flood
protectionandshouldaimtoestablishabalance betweenthe two. There are twoapproachesfor
addressingthisissue,whichinclude:
1 Structural Approach – Involvesimplementingfloodcontrol structures,suchasdams,weirs,
reservoirs,canalsetc.in orderto helpregulate waterflow;
2 Non-structural Approach –Thisshouldtake the form of floodpreparednessplanningand
deal withimplementingtechniques,particularlythroughgovernmentlegislation - flood
response,floodwarnings,stormwatermanagement,watershedmanagement,flood
proofing,etc.(STCRegional Planningand DevelopmentBoard,2016)
Hydrologicandhydraulicmodellingisatechnique thatcan be usedto bridge the gap between
structural and non-structural approaches,mainlydue totheirnumerical modellingcapabilities -
abilitytoestimate peakdischarges,catchmentarea,watervelocities,depthmeasurements,their
abilitytoprovide anunderstandingof the flow patternsandfloodingdurationsandanalysingflood
zone waterlevels(DelisandKampanis,2015; STC Regional Planningand DevelopmentBoard,2016).
However,the qualityof any numerical modellingsystemishighly dependentonitsdescriptive
capabilities,whichare primarilythe surface roughnesscharacteristicsandtopographicinformation.
Thiswill be analysedanddiscussedlaterinthe study.
1.1.1 Aims and Objectives
Aims
The aim of thisresearchpaper isto testthe validityof hydrauliclossesdescribedinthe CIRIA
guidance methodology,practicedinthe UnitedKingdomagainstthe Texasdepartmentof
transportation – Hydraulicdesignmanual methodology.The hypothesisis thatfornon-standard
culverts,the CIRIA guidance methodologypresentsinaccuraciesbyoverestimatingthe lossesand
resultingupstreamwaterlevels.The hypothesiswill initiallybe appliedtoa non-standardBurnley
Road culvertonthe RiverCalderinTordmorden,UnitedKingdomwiththe potentialtoextendthe

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assessmenttoother,regulartestcaseselsewhereinYorkshire.Itisintendedthatthese findingswill
helpimprove the representationof the culvertinletenergylossesinUK hydraulicmodelling
packages.
Objectives
In orderto make thiscomparison,analysisof real worlddatashall be undertakenthrough
the applicationof hydraulicmodellinginFloodModellerHydraulicModellingSoftware.The specific
objectiveswill be to:
1. Developabaseline hydraulicmodel of the testreachinFloodModellerPro.
2. Establisha rating,inorder to findthe flow forobservedlevelseries.Thisprocedurewill
involve undertakingiterationstoestablishthe BestManning’s,Low Manning’sandHigh
Manning’sandtestingthe ratingssensitivitytothese valuesandculvertinletlossvariations.
The Manning’sshall be takenfromthe recommendedManning’s‘n’valuesforchannels
(Chow,1959).
3. Once a range of observedinflowsare determined,these inflowswill be runthroughthe
hydraulicmodel andtestedagainstthe CIRIA inletcoefficient‘s’andthe Texashydraulic
designmanual inletcoefficients.Thisprocedurewill involveconstructingamatrix through
whichall the optionswill be simulatedagainsteachother. Twenty-one simulationsare
expectedfromthisprocedure.
4. Resultingwaterlevelsatthe testpoint(upstreamof BurnleyRoadculvert) will be
assessedforsuitabilityforeachof the three testevents.
5. Furthermore,recommendationswill be providedforthe mostappropriate culvertinlet
lossrepresentation.

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2 BackgroundReview
2.1 Relationship between Manning’s andRating Curves
Ratingcurveshave been,andstill are,a reliable meansof assessingthe relationshipbetween
waterlevelsandflowinopen channels.Atthe turnof the 18th
century,streamflow measurementin
natural structuresor man-made structuressuchas rivers,streams,irrigationditches,canals,partially
full pipesandwaterconveyance flumes,wascarriedoutusingconventionaltechniquessuchasthe
currentmetermethodandother,measuringtechniques(USGS,2016; Braca, 2008). These methods,
althoughappreciatedandnecessary,still bringaboutthe impracticalityof the directflow
measurementinopenchannels,especiallyduringflooding,becauseof the associatedunderlying
costs andthe laboriousprocessof extractinginformation.
Conventionalmethodsforachievingcontinuousriverflow measurementisthroughthe
applicationof gaugingstructureswithknownhydrauliccharacteristics.Althoughthismethodis
efficientandeffective;however,itismetwithaleatory(random)uncertaintiesarisingfromthe
changesinhydrauliccharacteristics,due tothe natural obstructions(woodydebris) inthe channel
bedprofile,while obtainingstage-discharge(National RiverFlow Archive,2016).So,for any given
rivercross-section,the accuracyof the stage-discharge relationdependsonthe following:
1. The cross sectional stability,i.e.anyinstabilityinthe channel crosssection,mostlydue to
scour/fill,backwaterandhysteresiseffects,aswellasvegetationandice,canpotentially
give rise toepistemicuncertaintiesand,therefore,resultinanunreliable ratingcurve.
2. The accuracy of stream gauge readings,i.e.aleatoryuncertaintiesarisingfromdifficulty
inobtainingaccurate waterlevel readingsduringthe peakfloodevents(McMillanand
Westerburg,2015; ISO,2010)
Literature fromsome authorsreportthat fora givenratingcurve,there are associatedglobal
uncertaintiesarisingfromvarioussourcesandthe degree of these uncertaintiessignificantlyaffects
the waterresource and floodestimates,aswell asthe model calibrationandmodel structure choice
(McMillanand Westerburg,2015). Hitherto,researcheffortsbyMcMillanandWesterburg(2015)
have expandedonthisphenomenonbydevelopingamethodof measurement,which,(1)
encompassesconstituentsassociatedwithrandomandepistemicuncertaintiesand(2) givesa
holisticgraphical representationof these uncertainties,basedonthe generationof multi-segment
powerlawstage-discharge curves.Thisapproachistherefore aimedatquantifyingbothaleatoryand
epistemicerrorsintoa single probabilityfunctionof the datapoint.Thismethodissetapartfrom
the orthodox methodwhichinvolvesquantifyingsuchuncertaintiesseparatelybasedonasetof
gauge pointsandsubsequentlyestablishingmultipleratingcurves,whichwouldthenbe compared
againsteach otherto identifycurvesthatfitperfectlythroughthe setof gauge points.Aswiththe
case of epistemicuncertainties,there isthe impracticalityof achievingasingle bestfitratingcurve
throughall the gauge pointssince the nature of sucha curve istime-variant.Likewise,quantifying
aleatoryerrorsthroughdata point likelihoodswouldsimplyinvolvegatheringthe productof all
likelihoodsforeachdata point.
PreviousstudiesbyPappenburgeretal.(2006) citedinMacMillan and Westburg(2015) and
researchby Kruegeretal.(2010) citedinMacMillan andWestburg(2015) expandsonthe data point
likelihoodquantitationandsuggestsminimisingthe distance betweenthe ratingcurve andthe
gauge pointsand/orsubstitutingthe normal distributionforapyramidal distribution,borrowedfrom

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fuzzyconcepts.Figure 2-1illustrateshow the probabilityof the datasetpointsisdeterminedfora
single-sectionstage-discharge curve.
Figure 2-1 Likelihood calculation of rating-curves
In orderto achieve ahighlevel of discharge accuracy,Leonardetal. (2000) suggestsrefining
the Manning’sequationsothatwhentryingto obtaina flow rate,twovariablesof the longitudinal
watersurface slope,aswell asthe hydraulicradiusneedisconsideredratherthanjustthe water
level alone,whichisoftenthe case.
One of the mostfundamental parametersgoverningopenchannelflow isthe surface
roughness.Thisroughness(alsoknownasManning) isdenotedbythe letter‘n’inhydrologicand
lumpedmodels.The Manning’scoefficientcan be determinedfromthe lookup Tablesorthrough
variousdigital estimationapproaches.Itiswell understoodthatforanygivenopenchannel witha
highManning’scoefficient,alowflowrate isexpectedandvice-versa.Thishasa directeffectonthe
discharge estimationandultimately,onthe nature of the rating-curve.The selectionof Manning’s
‘n’is oftenbasedonsoundengineeringjudgement,whichmakesthe estimationprocesssubjective.
Some level of engineeringexperience is,therefore,requiredwhenestimatingthesevalues.A few
approachesto estimate Manning’s‘n’include,1.Visual inspection,2.Physicallybasedinspection,3.
Optimisationtechniquesand4.Satelliteremote sensing(ArcementandSchneider,1990, citedin
Kalyanapuetal.,2009; Sellinetal.,2003, citedinKalyanapuetal.,2009). These approachesare
describedbelow:
1. Visual Inspection –Thisorthodox methodof inspectionofteninvolvesthe use of
photographsfromsite inspectionscoupledwithsurface roughnessbookvalues.This
technique is,however,limitedtosmall catchmentareasandthe data presentedisof an
intuitive understanding,thusleavingahuge marginforanalytical errors.
2. Physicallybased –Withthisapproach,the estimationof Manning’s‘n’isbasedon
graphical information,suchastopographicirregularities,watersurface wavinessand
vegetationdensity.
3. Optimisationtechnique –Thistechnique offersanobjectiveviewof the test,whichwould
otherwise be disregardedthroughanalytical biases(Kraijenhoff andMoll,1986). Asthere is
a correlationbetweenflow androughness,mappingtool websitessuchasNational River

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FlowArchive orShoothill Gauge Maps(Shoothill,2016) or evenvegetationdensity
measurementsusingparallel photographyandterrestrial laserscanningcanprovide a
comprehensive guideforcapturingflow data,channel configurations,vegetationelevation,
as well asotherhydrauliccharacteristics.
4. Satellite remote sensing –Surface roughnesscanbe determinedforlarge scale operations
usingsatelliteremote sensingtechniques.Inpractice,landcoverdatasetsare assigned
Manning’s‘n’valuesfromthe look-upTables.Literature fromauthorssuchas Chow (1959)
providesarange of roughnesscoefficientsforchannels,closedconduitsorcorrugated
metal pipesflowingpartiallyfullorat capacity.
ResearchbyLeonardet al.(2000) is aimedatimprovingextrapolationandmanaginginstability
throughratingcurve modellingusingManning’sequation,andhighlightsthe needtomodifyit.In
additiontoconsideringthe twovariables,the refinedequationshouldalsotake intoaccountboth
the hydraulicandgeometriccharacteristicsof the riverreach,whichwouldresultinimproved
discharge estimations.Hence,measurementinstrumentssuchasthe followingneedtobe
adequatelyinstalledandoperated:
1. Installingasecondstaff gauge upstreamwill provide anapproximationof the riverwater
surface slope.The gauge shouldbe fittedwithanautomaticstage recorder;
2. A downstreamtopographicalprofile shouldbe usedinordertoestimate the hydraulic
radiusduringhighflows.Hydrologypractitionersneedtobe mindful of the surface
roughnesssensitivitytoanychangesinthe hydraulicradius;forinstance,adecrease inthe
surface roughnesswill occur due toan increase inthe hydraulicradius;
3. Gatheringstreamgauge data at differenttimesandstagescanprovide informationof the
geometriccross-sectionof the downstreamreach.
Adoptingthismethodshouldallowmore reasonableestimationsof the continuouslychanging
geometricandhydrauliccharacteristicsof the riverreach.
The nature of a rating curve is definedbythe relationshipbetweenthe upstreamchannel gauge
and the downstreamchannel state.The flow velocityisinfluencedbythree different stationcontrols
(BRACA,2008):
1. SectionControl
2. Channel Control
3. Combinationof SectionandChannel Control
2.1.1 Section Control
There isa needtoascertainwhetherthe typesof hydraulicstructuressituatedonthe
downstreamof a channel,influencesthe upstreamlevel gauge heightanddischarge relation.These
hydraulicstructuresare inthe form of concrete fixtures,suchasflumesorweirs,butcan alsobe in
the form of any natural obstructionsinthe channel,suchasthe accumulationof woodydebrisor
evenrocksthat ultimatelyleadtothe narrowingof the channel crosssection. Figure2-2 illustrates
this.

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Figure 2-2 Section control (Source: Braca, 2008)
Floodingeventscause the gauge heighttorise,whichleadstosubmergence of the sectioncontrol.
Therefore,the sectioncontrol cannolongerinfluence the upstreamgauge heightanddischarge
relation,butisinsteadcontrolledbyanotherdownstreamsectioncontrol,surfaceroughnessor
hydrauliccrosssection.
2.1.2 Channel Control
Thiscontrol takesintoaccount the downstreamgeometricpropertiesof the channel profile aswell
as itssurface roughness,relativetothe upstreamgauge.The nature of the rating curve and channel
slope are inherentlylinked.Forinstance,forsteepchannels,the ratingcurve isgovernedbyashort
channel reachand forflat channels,the ratingcurve isgovernedbyalongerchannel reach.
SectionandChannel Control Combination
The transitionzone betweensection-control andchannel-controliswhere acombinationof both
controlsoccur overa shortlevel range. Figure2-3 graphicallyillustratesthe stage-dischargerelation
as shownbelow:
Figure 2-3 Control ranges in rating curve (Source: Braca, 2008)
Changesinstage-discharge relationshipare likelytocause a shiftinthe positioningof both
controlson the ratingcurve.It is,therefore importantthatthe waterflow characteristicsare fully
comprehended,inordertoconstructan accurate stage-discharge relation,especiallywhere either

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one of these control featureschange orwhere one ismore effectivethanthe other.Twoor more
controlsactingin syncis a rare occurrence.
Moreover,backwatereffectsare alsoanotherfactorto contestwithinstable andunstable
channels.Thiseffectmostlyarisesfromstructureslikedams,reservoirs,waterfallingoveravertical
drop,tributarystreamsor any objectsthatmay impede waterflow byeitherspeedingitupor
slowingitdown,thusaffectingupstreamlevelsandflows(EcologyDictionary.org,2008).
An unusual effectthatoccurs inthe flatslopedstreamsduringunsteadyflow conditions
knownas the hysteresisloop,ismainlycausedbyfluctuatingwaterlevelsinthe channel,leadingtoa
change in the watersurface slope. Figure2-4 graphicallyillustratesthiseffect.A higherdischarge is
experiencedwhere the watersurface slopeissteeperthanthe slope duringthe steadyflow
conditions.
Figure 2-4 Hysteresis loop effect (Source: Braca, 2008)
2.2 Factors to Contestwith When Interpreting the Stage-Discharge Relationship
Braca’s (2008) findingsregardingthe issuesthatdefine the stage-discharge relationship,seemtobe
centredparticularlyonthe factorsthat cause adverse effectsonthe ratingcurve,namely;changesin
cross-sectional geometry,woodydebris(potentiallyleadingtoblockage andnarrowingof the stream
path),the presence of aquaticvegitation,backwatereffects,scourandfill,dynamicdischarge
patterns,ice andincrease or decrease of alluvialstreambedduringthe floodingevents.The Figure2-
5 belowprovidesagraphical illustration(ratingcurve) of thesedifferentphysical processes(Herschy,
1995, citedinBraca, 2008).
The dynamicdischarge pattern,backwatereffectsandthe waterflow toorfrom the
floodplainoverbankareas,all showthe characteristicloopedratingcurve.A frameworkfortackling
these factorsincludesanapproximationof the watersurface slope orthe speedof waterat the
gauge.

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Figure 2-5 Rating curves of different physical processes (Source: Braca, 2008)
2.3 Particular Circumstances that Affect Rating Curves Sensitivity
2.3.1 Ice Covered Rivers
Freezingandthawingeffectsof riversimpactsthe hydraulicradius,surface roughnessand
cross-sectional area.Underfreezingconditions,anice layerformsonthe water surface and
increasesthe hydraulicradiusandsurface roughness,withasimultaneousdecrease in the rivercross
sectional area,all of whichaffectsthe nature of the ratingcurve.Gauging the thawingeffectis
however,metwithdifficultyininterpolationbetweendischarge measurementandinmostcases,
callsfor the stage,temperature andprecipitationrecordsof the testarea(Herschy,1998).
2.3.2 Coastal Rivers
The water level incoastal riversisgovernedbyboththe flow discharge anddownstream
tidal wave activity.Boththese effectsinterfere withthe stage-discharge relationship.Analysisof the
tidal effecttypicallyinvolvesthe theoretical applicationof the equationsof unsteadyflow,whichisa
widelypreferredapproach(Braca,2008).
2.3.3 Theoretical Computations
Thisis a time andcost effective meansof obtainingstage anddischarge data.Theoretical
computationsare a meansforestablishingstage-dischargerelation,where currentmeter
measurementsfall shortandare conductedusingthe channel configuration,surface roughness

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approximationandassigneddischarges.A ratingcurve can thenbe derivedusingequationsof
unsteadyflowandcanbe conductedwithoutthe needof anystage-discharge measurements.
2.4 Culvert Design
Culvertsare hydraulicstructuresdesignedtopasssteadywaterflow throughanembankment
(Wildon,2013). The differenttypesof culvertstructuresinclude circular,rectangularorboxed,
piped-archandelliptical,archor complex (Hydraulicdesignmanual,2016). There isa framework
throughwhichthe culvertscontrol the discharge capacity.These are inletcontrol oroutletcontrol
and bothcontrolscan eitherbe insubmergedorunsubmergedstates(FishXing,2006).
2.4.1 Inlet Control
A culvertisunderinletcontrol duringthe supercritical flow conditionsandthe factors
affectingdischarge throughsuchastructure are itsentrance characteristicsi.e.,inletedge,cross-
sectional areaandthe shape of culvert,inadditiontothe headwaterdepth(LMNOEngineering,
ResearchandSoftware Ltd,2010). Culvertcapacityisnotinfluencedinanyway by the culvert
roughness,lengthof culvertoroutletconditionsduringthisstate.
Duringhighflowsthe culvertcanoperate as an orifice,particularlyif the outletconditions
permitthe free flowof waterasillustratedin Figure2-6 below (Hydraulicdesignof improvedinlets
for culverts,1972).
Figure 2-6 Inlet Control with inlet submerged (Source: Hydraulic design of improved inlets for culverts, 1972)
Conversely,aculvertentrance maybe unsubmergedwhere itactsas a weirduringlow flows
(Creamer,2007). Figure 2-7 illustratesunsubmergedinlet.
Figure 2-7 Inlet Control with inlet unsubmerged (Source: Hydraulic design of improved inlets for culverts, 1972)
2.4.2 Outlet Control
A culvertoperatesunderoutletcontrol duringsubcritical flow conditionsandtherefore,discharge is
influencedonlybythe surface roughnessandfriction.Unlike the inletcontrol configuration,flow is

18
controlledbythe downstreamendof the culvert.Culvertsflowingunderoutletcontrol have entire
or partial lengthof the barrel filledwithwater.Full flowstate isachievedwhenthe waterlevel,
immediatelydownstreamfromthe culvertoutlet(alsoknownastailwater) isabove the culvert
barrel diameter.The designof culvertsshouldbe insucha waythat the tailwaterlevel isaccounted
for; itshouldnotbe significantlyhighoritcouldleadtofloodingonthe upstreamend,norshouldit
be too lowthat itcan potentiallyleadtoerosionof the bank(Engineeringcivil.com,nodate).The
partiallyfull culvertbarrel conditionoccurwhenthe tailwateriswell belowthe culvertcrown
(Drainage manual,2002). The Figure 2-8 showsthe differentoutletcontrol states,subjecttothe
headwaterandtailwaterlevels.
Figure 2-8 Illustration of different outlet control states (Source: Hydraulic design of improved inlets for culverts, 1972)

19
Table 2-1 Main factors affecting Inlet and Outlet control (Source: FishXing, 2006)
Dependingonthe factorssummarisedin Table2-1 above,the culverthasthe potential to
eitherfunctionasa weir,orifice orpipe (dependingonthe pressure gradientof the flow) (Guala,no
date).
A conservative approach towardsculvertdesignshouldaimtoaddressthe following:
1. A cost effective designshouldalwaysbe sought;
2. Minimal flowshouldbe achievedthroughoutthe designnetwork;
3. Where culvertshave perchedoutletsorinletdrawdown,scourprotectionmeasuresshould
be implemented(Hanson,2010).
2.5 Energy Dissipation
Culverthydrauliccapacityandperformance isinextricablylinkedandcanbe improved
throughmodificationof the inletgeometriesandheadwaterlevels(Hydraulicdesignof improved
inletsforculverts, 1972). Asflowisfunnelledintoaculvertopening,energydissipationisobserved
at both inletandoutlet.Thisenergydissipationissubjecttorelative constantfrictionaswell as
continuoushaphazardheadlosses(Pazwash,2016).
2.5.1 Conventional Systems
Conventionalcircularculvertinletscanbe customisedtoachieve bothenergyefficiencyand
performance,aswaterisfunnelledintothe culvert.The culvertinlettypesthatpermitsthis
hydraulicadvantage are thin-edgedprojecting,square-edgedandgroove-edged.Headwaterdepth
and inlettype governsthe capacityof these three inletgeometrieswithaclearcorrelationbetween
the performance andflowcontraction,inwhichahigherflow contractionisachievablethrough
increasedheadwaterdepth(HydraulicDesignof ImprovedInletsforCulverts,1972). In termsof
performance,the groove-edgedprojectingtype farexceedsthe square-edgedprojecting,whichin
turn performsbetterthanthe thin-edgedprotrudinginletsatanygivenheadwaterdepth.The Figure
2-9 givesanillustrationof the flowcontractionsandbarrel capacities,forthe thin-edged,square-
edgedandgroove-edgedprojectinginlets,labelled1,2 and 3 respectively.

20
Figure 2-9 Thin-edged, square-edged and groove-edged flow contractions (Source: Hydraulic design of improved inlets for
culverts, 1972)
2.6 Improved Systems for CulvertInlet andOutlet
Mitigatingenergylossesandachievinghydraulicefficiencythroughoutthe culvertnetwork
requiresimprovementsof the culvert inletedgesandculvertoutlet.Thisisparticularlyimportantas
the inletedgesinfluence the flow byconstrictingit,whichultimatelyleadstoareductionineffective
cross sectional areaof the culvertandthus,resultsinpoor performance (Drainage andfloodcontrol
district,2001). Similarly,culvertoutletsare susceptible toturbulence issuesbecauseof the abrupt
changesinthe flowdirectionorevenflow expansionsandultimatelyleadstoenergydissipations,
scouring,bankerosionandmaterial degradation,whichinturnisinfluencedbythe tailwater(Osman
and Adam,2015; Handbookof Steel Drainage andHighwayConstructionProducts,1984).
2.6.1 Bevel-edged Inlets
Whenthere isan abrupt change inthe waterflow due toa change ingeometry(cross
section),energylossisexperiencedatthe venacontractadue to the contraction(McDonald,2005).
The placementof bevelsatthe crownof the culvertreducesthe flow contractionof the culvertinlet.
It issuggestedthatbevelsshouldbe usedoninletcontrolledculverts,astheyhave the potentialto
achieve increasedcapacity.Thishowever,onlyholdstrue forbevelsfittedtosquare edgedinlets
resultingina5 – 20% increase incapacity(HydraulicDesignof ImprovedInletsforCulverts,1972).
The type of constructionmaterial alsoplaysacritical role inculvertperformance.Culvertbarrels
constructedto a concrete finishandcircularconfigurationeliminatethe needforbevelsdue tobeing
alreadyintegratedwithasocket(bell) end,whichissimilarinfunctiontoabevel fitting.Thisallows
for a reducedentrance losscoefficient(AmericanConcretePipe Association,2004).The Figure 2-10
showsthe side elevationprofileof abevel fittedatthe culvertinlet.

21
Figure 2-10 Bevel placement (Source: Hydraulic design of improved inlets for culverts, 1972)
2.6.2 Side–Tapered Inlet
The side taperedinletis20%more efficientinflow capacitythanthe bevelled-edge inlet.It
isalso 100% more efficientthanthe standardsquare-edgedinlet(DeeboandReese,2003).The
geometricpropertiesof thisinletare suchthatthe inletface extendsfromaheightrelativetothe
barrel. Figure2-11 givesan illustrationof abox section,whichalsoindicatesthe control sections.
Figure 2-11 Side-tapered inlet (Source: Hydraulic design of improved inlets for culverts, 1972)
The throat control sectionregulatesthe flow contractionbyreducingthe degreeof the flow
and providingmore headatthe inlet.The increasedcapacitycanbe mainlyattributedto‘fall’atthe
entrance (HydraulicDesignof ImprovedInletsforCulverts,1972).

22
2.6.3 Slope-Tapered Inlet
The slope-taperedinletcarriesoutthe same functionasthe side-taperedslope,onlymore
efficiently.Thisinlettype incorporates three control sections - the inletface,the bendandthe
throat.The bendislocatedbetweenthe inletface andthroat.Itis at a minimal distance fromthe
throat and allowsaneutral influence onthe flow.The slope-taperedinletslightlyout-performs the
side-taperedinletbyprovidingadditionalheadbecause the ‘fall’betweenthe inletface andthroat
resultsina flatbarrel slope.Thisinlettype allowsforanincreasedhydrauliccapacityatany given
waterelevation,inbothcircularpipe culverts andbox culverts(ConnDOTDrainage Manual,2002;
HydraulicDesignof improvedinletsforCulverts,1972). Figure 2-12 showsa slope-taperedinlet
profile.
Figure 2-12 Slope-tapered Inlet (Source: Hydraulic design of improved inlets for culverts, 1972)
2.7 Culvert WingWalls
Musete and Ho (2012) asserton the importance of the wingwall flare anglesforproviding
hydraulicadvantage (minimisingheadlosses).Culvertwingwall performance isinfactgovernedby
concrete culverttype i.e.Pre-Castreinforcedconcrete orCast-In-Place reinforcedconcrete.The
findingsseemtosuggestthatif bothculverttypesutilisedflaredangles,the Cast-In-Place will always
outperformthe Pre-Castconcrete culvertasshowninthe Figure 2-13, where CIPandPC are Cast-In-
Place and Pre-Castconcrete,respectively.

23
Figure 2-13 Performance curve illustration of Cast-In-Place concrete and Pre-Cast concrete (Source: Musete and Ho, 2012)
The authors advise thatfora culverttobe fittedwithwingwalls,itisimportantthat the
cross sectional areaof the channel isincreasedaroundthe inlettoanarea suitable forthe assigned
wingwall flare angle.This,howeverleadstosedimentationissuesandcanaffectthe culverts’
hydraulicperformance (Ho,2010, citedinMusete and Ho, 2012).
Culvertendwallsserve toenhance the structural integrityof the pipe,aswell asensure
channel bankerosionandscouringcontrol.The Figure2-14 illustratestypical headwallsand
endwallsforculverts(Ahmed,2006).
Figure 2-14 Typical culvert headwalls and end walls (Source: Ahmed, 2006)

24
2.8 Culvert Outlet
The culvertsstructural integrityiscompromisedwhenscouringandmaterial degradation
occurs at the downstream.OsmanandAdam(2015) have suggestedmitigationmeasureslikethe
improvementof the culvertgeometryandassessingthe turbulentjetandsoil properties.These
parameterspayparticularregardto the velocityof the incomingupstreamflow,soil particlesize,
shearstresscausedby turbulentjetandalsothe shearresistance,all of whichdefine the erosion
cycle.The strong correlationbetweenturbulence andthe formationof scouringpoolsinnarrower
channelsisreported.Itcan be observedthatthe turbulence isreduceddue tothe interaction
betweenthe flow andchannel bank,whichresiststhisflow.Thus,areducedturbulenceleadstoa
decreasedscouringdepth.
As previouslymentioned,the geometriccharacteristicsof the culvertoutletalsohave an
effectonthe depthandwidthof the scour pool.Semi-circulargeometrywill provide aslightlylonger
service life thanalinearapron,asthe scourpoolsformedhere will be shallowerandnarrower
(OsmanandAdam,2015). The additionof wingwallstoboththe inletandoutletcouldpotentially
eliminatethe formationof scouringpoolsandbankerosion.The wingwallsdonotonlyprovide
engineeringadvantage,butalsoofferhydraulicadvantage forenergyloss,dependinguponthe flare
angle.If the flare angle fordownstreamculvertoutletis80
andthe lengthof the wingwall istwice
the diameterof the outlet,there willbe areductioninheadloss(LiuandZhu,2000, citedin
HabibzadehandRajaratnam,2016).
2.8.1 Culvert Outlet Energy Loss
Researchfindingssuggestanumerical approachtoevaluate the outletlossesandcanbe
derivedfromthe Borda-Carnotexpression,whichisasimplifiedenergyequation.(Tullisand
Robinson,2008, citedin HabibzadehandRajaratnam, 2016). However,amore recentstudyhasbeen
undertakenonthe basisof theoretical conceptsand involvescomparingthe kineticenergyformedin
a turbulentjettothe submergedoutletflow.Turbulentjetphenomenonoccurswhenamovingfluid
meetswithasimilarstaticfluidandas a result,turbulence iscausedbecauseof the force between
the two fluidsthatsubsequentlyresultsinkineticenergy(e.g.,riverflowingintoalake) (Cashman-
Roisin,2014). The kineticenergywithinthe flow canthenbe assessedwithrespecttoitsposition
relative tothe outletandtherefore,anyenergylossesobserved(HabibzadehandRajaratnam, 2016).
2.9 Effectsof Culvert Barrel Number
As aforementioned,thereare awide range of culvertstructuresi.e.circular,rectangularor
boxed,pipedarch,elliptical orcomplex andeachof themisusedin a differentconstructionscenario.
More oftenthannot,culvertperformance isgovernedbythe barrel number.Accordingtoaresearch
by Musete andHo (2012), there isno difference inperformancebetweensingle pre-castreinforced
concrete barrelsandmultiple pre-castreinforcedconcrete barrels,operatingunderunsubmerged
flowconditions.However,thisdoesnotnecessarilyholdtrue undersubmergedflow conditions,
especiallywhere highflowsoccursandif the channel slope material issteel.Furthermore,this
difference in discharge isof aslightlylesserextentandsmallerinmildchannelslope.The authors
furtherdiscussandsuggestthatthe cast inplace culvertswitha 300
flaredwingwall are more
efficientathandlinghighflows,astheyfunnel flowstothe culvertentrance forbothsingle and
multiple barrels,ateitherasteepormildchannel slope.

25
2.10 Culvert Rating Curve
Establishingaculvertratingcurve isa meansthroughwhichculvertcapacitycan be evaluatedunder
varyingstage levels.Asculvertdesignisbasedonthe estimatedflows,one of the challengesisbeing
able to gauge the governingcontrolsata givenpool stage i.e.inletcontrol oroutletcontrol fora full
range of flow.So,culvertratingcurvesare usedto checkif the control shiftsfrominlet tooutletor
the otherway aroundand predictto some degree,anypotential repercussions,where floodriskis
concerned(Crowder,2009).The Figure2-15 illustratesthe performance curvesforculverts
operatingunderinletandoutletcontrol ata givendesignstage.Itmustbe notedthata combination
of boththe control conditionsresultsinthe overallperformance curve,asshowninthe subsequent
Figure 2-16.
Figure 2-15 Performance curves of control conditions (Source: Hydraulic design of highway culverts, 1985)
Figure 2-16 Performance curves of control conditions (Crowder, 2009)

26
2.11 Materials
The constructionmaterialsusedforculvertconstructionare concrete,reinforcedconcrete,
galvanizedsteel,aluminiumorpolyvinylchloride;andthe selectionof the materialsisbasedonthe
economicevaluationthatshouldconsiderconstructioncosts,topographyof the site,hydraulic
efficiency,span,geotechnical characteristics,climatological andwatershedcharacteristics,
geotechnical characteristicsof soil orstate policy(FishiXing,2006).The twomost commonmaterials
usedare corrugatedmetal andconcrete.Thisisprobablybecause of theirpotential toachievea
varietyof advantages.Corrugatedmetal pipespresentthe followingadvantages:
1. Low maintenance atthe inlet;
2. Comparedtotheirprojectingentrance counterpart,the likelihoodof damagesfrom
maintenance workorfromaccidentsislow;
3. Increasedhydraulicefficiency(Drainage CriteriaManual,2001).
The advantagesthat arise fromthe applicationof rigidpipesare:
1. As aforesaid,the socketendconfiguredontoconcrete pipeshelpsachievereduced
energylosses,whichinturn,allowsthe smallerdiameterpipestobe usedincontrastto
othermaterial types;
2. Concrete pipeshave nominal internaldiameters,whereascorrugatedmetal pipesare
over5% smallerthannominal.Thisisparticularlyimportant,whenitcomesto
evaluatinghydrauliccapacity;
3. From an economicperspective,rigidpipessystemshave beenproventocontinuously
gainstrengthovertheirlife cycle (AmericanConcrete Pipe Association,2004; Concrete
Pipeline SystemsAssociation,nodate).
2.12 Culvert Positioning
A fundamental considerationinculvertplacementisensuringitsalignmentisrelative tothe
stream.The rationale behindthisisthe eliminationof turbulence causedbyabruptchangesinflow
directionatthe culvertentrance andculvertexit.Therefore,directentryandexitof flow througha
culvertcan be achievedthroughaskewed alignmentoranoverall change of the channel (Handbook
of Steel Drainage andHighwayConstructionProducts,1984). Althoughthisrequireshighcostsdue
to the increase inculvertlength,thiscanbe justifiedthroughthe future preventionof scouring,
incisionoraggradingissues(WisconsinDepartmentof Natural Resources,2016).
Anotherfactorimperative toculvertalignmentisthe grade line choice.The Figure2-17 and
Figure 2-18 illustrate the methodsof selectingthe alignment.

27
Figure 2-17 Culvert placement through grade line positioning (Source: Handbook of Steel Drainage and Highway
Construction Products, 1984)
Figure 2-18 Culvert placement through grade line positioning (Source: Handbook of Steel Drainage and Highway
Placementof culvertsatroadwayintersectionsshouldbe paralleltothe roadwayditchas
showninthe Figure 2-19 and shouldbe designedinamannerthat itssize accountsfor debris,
blockage andfailure duringfloods.

28
Figure 2-19 Roadway culvert positioned parallel to roadway (Source: Handbook of Steel Drainage and Highway
2.13 Hydrographs
Hydrographsare a graphical representationof how waterbodiesrespondto hydrologic
variables,particularlyrainfall,overagiventime period.There are differenttypesof hydrographs,
such as:
 Streamdischarge hydrographs – Theyshow the extentbywhichwaterlevelshave risen,
inrelationtoa datumpointovera giventime;
 Water temperature hydrographs –Theyshow change inwatertemperature throughthe
day;
 Streamdischarge hydrographs – Theyshow how discharge varieswithtime;
 pH hydrograph – This showschangesinwaterpH overtime;
 Specificconductance hydrograph –It showselectriccurrentthroughwaterovertime;
 Precipitationhydrograph –Thisshowsthe amountof precipitationovertime
(Geology.com, nodate).
For the purpose of thisstudy,stormhydrographswill be the primaryfocus.
2.13.1 Storm Hydrographs
Storm or flood hydrographsare chartsusedto illustrate discharge inachannel overatime
period.Thistime periodisinmostcasesrelativelyshorti.e.hoursordays,ratherthan weeksor
months.The discharge occursthrough differentwaterbodies,suchasrivers,lakes,streamsetc.and
theircapacitiesare subjecttohydrologiceffects(InternetGeography,2015). A storm hydrograph
has dependantvariables,whichare discharge (measuredincumecs) andrainfallevent,andan

29
independentvariable,whichisisthe time period.The discharge isrepresentedbyaline graph,while
the rainfall eventisrepresentedbyabar graph. The SI unitsforthe discharge,precipitationandtime
periodare m3
/s,mm andhours,respectively(Jackson,nodate).Anillustrationof astorm
hydrographcan be seenin Figure 2-20.
Figure 2-20 Storm hydrograph (Source: Jackson, no date).
2.13.2 Interpretation of Storm Hydrographs
As seeninthe Figure2-20, a storm hydrographisdefinedthroughanumberof stages,namely,
1. Risinglimb–This isthe rise in riverdischarge due togroundand soil water,aswell asany
surface run off
2. Recedinglimb –Thisindicatesthatthe channel isexperiencingafall indischarge
3. Basinlag time – Thisis the delayor time differencebetweenthe peakprecipitationand
peakriverflow
4. Rainfall intensity –Representedbyaseriesof bargraphs showingthe highestandlowest
rainfall amountsonthe catchment
5. Peakdischarge – The highestpointof flow ina channel
6. Base flow – Normal riverflow(Ashton, 2001; Jackson,no date)
2.14 Factors Affecting Storm Hydrographs
The representationof hydrographsmayvarydue tocertainfew physical factors - topography,
geotechnical characteristics,vegetationandthe precipitationandtemperature.
2.14.1 Area and Channel Slope
Large catchmentbasinsinterceptasignificantamountof precipitationandthereforehave a
greaterdischarge.Thisismainlygovernedbythe shape of the basin.Itisseenthatconventional
circularbasinshave a higherpeakdischarge,buta longerlagtime,aswater hasto travel a longer
distance toreach the river,as comparedto elongatedandnarrow shapedcatchmentbasins.

30
Furthermore,asteeptopographyalsohasan influence onthe shape of the hydrographas wateris
able to travel downhill faster, resultinginashorterlagtime and higherpeakdischarge.Lastly,
catchmentbasindensityhasaneffectonthe lag time particularlyforthe basinswithawide network
of streamsandrivers,whichultimatelyleadstoa shorterlagtime (Jackson,nodate)
2.14.2 Geotechnical Characteristics
The hydrographis influencedbythe typesof soil (suchassandy,clayor silt) andthe
differentrocktypes(suchas permeableorimpermeable) thatsurroundariver(Ace Geography,no
date).Waterinfiltrationdoesnotoccurin impermeable rocksandclaysoilsdue tothe closely
packedsoil particlesandasa result,surface runoff occurs,whichresultsinahighpeakdischarge and
a short basinlagtime.Onthe otherhand,permeable rockshave looselypackedsoilparticles,i.e.
sandysoils,whichincrease infiltration.The peakdischarge isreducedaswaterinfiltratesthroughthe
soil andis storedwhilstthe basinlagtime isincreased(Jackson,nodate)
2.14.3 Environment
Lush vegetationonriversurroundingsislikelytoabsorbconsiderableamountof water,
whichisthenlostduringthe watercycle process.Dense vegetationimpedessurface runoff andasa
result,the channel peakdischarge decreasesovertime whilstincreasingthe lagtime (Internet
Geography,2015; Jackson,no date).
2.14.4 Precipitation and Temperature
Storm hydrographsare influencedbythe type of precipitationi.e.the effectsof snow,hail,
sleetorrain,are alsoinextricablylinkedtotemperature rate.Rainhasthe shortestlagtime as
comparedto snow,whichhas much greaterlagtime.Thisisbecause the snow has to meltbefore it
can be receivedbythe river.The rate at whichthe snow meltsistemperature dependenttherefore,
at highertemperaturesthe snowwill meltfasterandthe basinwill have anincreased peakdischarge
(InternetGeography,2015)
2.14.5 Land usage
Storm hydrographsare sensitivetohumanactivity,particularlyinurbanandrural areas. The
builtenvironmentinurbanareasusuallyhasroadsand pavements,whichare coveredwith
impermeable materials,suchastarmac or cement.Theydonot allow waterinfiltration,which
increasesthe surface runoff andinturn,increasesthe peakdischarge,whilstgraduallydecreasing
the basinlag time.Conversely,forrural locationswithfarmland,farmingpractice of ploughing
parallel tohill slopesmustbe avoidedinordertopreventchannels,whichcancreate pathwaysfor
rainwatertoreach the riverfaster.
2.15 CIRIA Guidance and Hydraulic Design Manual – TexasDepartmentof
Transportation
CIRIA isthe research andinformationnon-governmental bodycommittedtoaddressing
variousissuesinsustainabilityandthe builtenvironment.Thisorganisation,formallyknownasthe
ConstructionIndustryResearchandInformationAssociationinthe UnitedKingdom, offers
authoritative informationanddesignguidancepublicationsonculvertdesignandoperation(CIRIA,
2016).
The CIRIA culvertdesignandoperationmanual 2010 isa comprehensiveguide thatcoversan
array of constructionandmaintenance concernsthatpertainto culverts,more specificallywith

31
regardsto inspections,assessments,maintenance,repair,replacementandremoval of existing
culvertsoverthe life cycle.Thismanual offersguidance fordesignof culverts,butdoesnotcoverthe
structural designing(Balkhametal,2010). Onthe otherhand,the hydraulicdesignmanual produced
by the TexasDepartmentof Transportationisconcernedwithaddressingbothhydraulicand
structural designof culverts.Unlike the CIRIA guide,itgivesadetailedguide onconstructionand
selectingappropriateculvertinletconfigurations,whilstconsideringvariablessuchascosts i.e.
capital,annual andlife cycle costs,location,installationprocessandmaterial durability(Garcia,
2016). In thisstudy,the focusis onthe culvertentrance losscoefficientsrecommendedinboth
manuals,whichwill be testedagainsteachotherinorderto prove the hypothesis.
2.15.1 Flood Simulation Software
Floodmodellingforhydrological analytical purposeshasevolvedsignificantlyovertime,
since the earlyworksof Ross (1921), Zoch (1934), Richards(1944) and Claark(1945) (all citedin
BevenandHall,2014). Theircontributiontothisfieldof studyservedasblueprintandinspiredthe
worksof Stoker(1957) and BevenandHall,2014, duringthe start of the digital eraandwhose
contributiontodevelopingdetailedhydrological andhydraulicmodelsinvolvedthe solvingof Saint
Venantequationsoncomputer(BevenandHall,2014). Since then,continuedeffortsinimproving
floodinundationmodels throughcomputational meanshasbeensoughtbynumerousresearchers
and byhydrologypractitionerstopresenttime withthe possibilityof 1D,2D and even3D
computational codes,whichare beingusedtosolve complex andspecificissues.Althoughthese
researcheffortsare appreciatedandnecessary,theyare,howevermetwithagreat degree of
uncertaintycausedbyerrorslike:
 Model structural errors arisingfromcombinednumerical issues,i.e.numerical stabilityor
numerical diffusionandconceptual model errors
 Multiple specificationsof parametersfordifferentelements
 Errors in detailingthe initialandboundaryconditionsof the element
The Figure 2-21 illustratessourcesof uncertainties,associatedwiththe floodcalamitymanagement
models.
Figure 2-21 Sources of uncertainty in flood risk management models (Source: Beven and Hall, 2014)

32
It isimportantto note that notall uncertaintieshave atremendousimpactonthe model
simulations.Leedal etal (2010) (citedinBevenandHall,2014) demonstratedamethodologyto
predictthe uncertaintyinfloodriskmaps,usingthe GLUE technique,whichwasbasedondatafrom
a major floodingeventinCarlisle Englandof January,2005. Priorto thisevent,aninitial discharge
estimate was establishedandinputina hydraulicbaseline model of the testreachinLISFLOOD
modellingsoftware.Itwasthenfoundthatthisdischarge estimate wassimilartothatof the survey
data collectedafterthe flooding.The initial dischargeestimate wasthenrevisedandincreased,
whichagaingave similarresults,althoughwithdifferentcoefficientsof roughness.Thisconcluded
that alteringhydraulicmodelsthisway,i.e.byincreasingthe scale of the eventthroughdischarge
calibration,willultimatelyaffectthe dependentvariables,whichinthiscase are the varyingfriction
lossesatdifferentflowsanddepths.The following Table2-2showssourcesof uncertaintywith
aleatoryandepistemicerrors.

33
Table 2-2 Sources of uncertainty
FloodmodellerProisa floodmodellingsoftware integratedwith1Dunsteady/steadysolver,
2D ADI(AlternatingDirectionImplicit) solver,2DTVD (Total VariationDiminishing) solverand2D fast
solvercomputationcodes,to aidhydrologypractitionersinovercomingcomplex floodrisk
managementchallenges(FloodModeller.com, 2016).Modellingof culvertsusingthissoftware
utilisesdefaultcoefficientsextractedfromthe CIRIA designguide.Thesecoefficientscanbe changed
inorder to suitthe user’sneeds.There ishowever,animpendingneedtoupdate these coefficients
as theytendto produce highheadlossesatculvertinlets(seeAppendix A onuserforumlogs).Thisis
to be analysedindetail inthe laterchapters.
Flood modellerprohasset the standardfor hydraulicmodellingpackagesinbothEurope
and non-Europeancountries.One particularfeature thatsetsthissoftware apartfromother
modellingpackagesisits2D modellingcapabilities,i.e.2DTUD (Total Variation Diminishing),which
givesa more accurate calculationof flow velocitiesandwaterlevels,especiallywhere abrupt
hydraulicchangesoccurand alsoallowsincreasedstability.Thisfeature isparticularlyimportant
whenassessingthe hydrauliccapacityof culverts(Jantzenetal,2015).

34
3 ResearchGap
The previouschapterreviewedthe remarksof differentauthorswithregardstoculverthydraulic
designandachievinghydraulicefficiency,intermsof minimisingenergylosses.Pastliterature
discussedthe implicationsof coefficientssuchasManning’s‘n’(forsurface roughness) andculvert
entrance losscoefficientsonthe nature of ratingcurves.The chapterconcludedwithabrief review
of the modellingsoftwarepackage,FloodModellerProanditsuse of the CIRIA methodologyfor
culvertmodelling.
No investigative researchhasbeenconductedforassessingthe inaccuraciesinenergylossesbrought
aboutfrom the CIRIA designmanual culvertentrance losscoefficients.Asmentionedpreviously,
these coefficientsdescribedinthismanual resultinoverestimationsof energylosses,whichleadsto
an increase inupstreamwaterlevels.Appendix A extractedfromthe communityforumonthe
official floodmodellersuitwebsite indicatesthe impendingneedtorectifythisissue.

35
4 ResearchMethodology
4.1 Introduction
The overall purpose of thisstudyisto testthe validityof the hydrauliclossesdescribedwithin
the CIRIA guidance.Thiswill be done byassessingthe performance of differentculvertinlet
structure configurationsandtheirresultingheadlossesunderflow conditions.Thisstudyadoptsa
fourfoldresearchapproach.Itaimsto:
1. Developabaseline model of the testreach
2. Establishratingcurvesfromobservedlevel seriesforthree floodevents,
3. Run simulationsfortwotestscenarios,one where the observedinflowsare testedagainst
CIRIA inletcoefficients,andanotherwhere the observedinflowsare testedagainstthe
HydraulicDesignManual coefficients
4. Assessresultingwaterlevelsatthe testpoint/level gauge sitesforsuitabilitywiththe
differentfloodevents.
Therefore,thischapteraimstopresentthe researchdesign,datacollectionanddataanalysis
procedures,alongwiththe conceptual framework.The studyintendstoaddressthe following
researchquestions - (a) Whatimplications,if any,dothe differentManning’sroughnessand
structure inletcoefficientcombinationshave onupstreamwaterlevels?(b) Doesthe CIRIA
configurationpresentoverestimatesof peaklevelsandcanit be improved?
4.2 Instruments
Thisresearchwas conductedusingacombinationof surveydataand the hydraulicmodelling
software package,FloodModellerPro(FloodModeller.com, 2016).The surveydatagatheredwasin
the form of CVPtopographical surveydata,gauge station readings,courtesyof the environment
agencyand a videorecording(Appendix B) of the floodlevelsforone of the floodevents.The Flood
modellerProsoftware utilisesequationsderivedfromthe CulvertDesignManual (1997)
methodologytodefine differentculvertcontrol modes,whichare usedindeterminingenergylosses
experiencedataculvertinletsandculvertoutlets.The FloodModellerProsoftware input
parameterscan be changedto be basedon the methodologycontainedinthe HydraulicDesign
Manual,whichin turncan allowcomparisonbetweenthe performancesof the twomethodologies.
4.3 Research Design
4.3.1 Stage 1
The researchtestsite is the Burnleyroadculvertonthe riverCalderinTodmorden,United
Kingdom.Recently,thisculvertwassubjectedtohighpeakfloodlevelson12 November2015, 12
December2015 and BoxingDay2015. Figure 4-1 maps outthe locationof thissite.Forthe
mentionedfloodevents,descriptionsof the upstreamwaterlevelsforthe BurnleyRoadculvert
eventsare summarisedas follows:
 BoxingDay2015: Videorecordingsindicatepeaklevelsoverlappingtopof the wall at the
CVPoutletlocation.The locationof the CVPoutletisshowninthe Figure4-1. A video
recordingwastakenat approximately10AMon 26th
December2015.
 12 December2015: Peakfloodlevelswere notobservedhowever,there wasprobably
no overlappingof waterlevelsonthe bank(at the low spoton the rightbank) at the CVP
outletlocation.

36
 15 November2015: The peakfloodlevel reached‘’twostone courses’’fromthe topof
the bank at the same location.
Figure 4-1 Location of Burnley road culvert on the river Calder, Todmorden (Source: Google maps, 2016)
CVPtopographical surveydataprovidedbythe environmentagencyallowedforthese
descriptionstobe translatedintomaximumwaterlevel estimates.Appendix Cshowsthe recorded
floodlevelsfor12th
November2015, 12th
December2015 andBoxingDay floodevents.Asthere was
onlyfloodleveldatatowork with andnot flows,the upstreamanddownstreamboundary
conditionswere configuredasStage – Time boundaryconditions(HTBDYS),ratherthanFlow-Time
boundaryconditions(QTBDYS) onFloodModellerPro.Thismeantthatthe levelswouldbe usedfor
establishingratingcurves,fromwhichinflowswill be derived.The EnvironmentAgency(2016)
provideddataof the recordedlevelsforthe upstreamanddownstreamgauges(Appendix C),which
allowedthe observationof the date andtime at whichmaximumwaterlevelsoccurred.This
informationwouldhelpdetermine the time stepstobe assigned(forwhenmaximumwaterlevels
occurred) intoFloodModellerProforthe deferentfloodeventsforrunningthe model effectively.
The firststage inbuildingahydraulicmodel isto aimto achieve amodel thatrepresentsa
single channel i.e.anunbranchedriverreach.Inthe case of the Burnleyroadculvert,there isa
junctionthatbranchesintothe Central Vale parkreservoir,immediatelybefore the culvertinlet
structure as showninthe Figure 4-2. The hydraulicmodel will notconsiderthisjunctioninthe
analysis,asitwas closedoff duringthe floodingevents.

37
Figure 4-2 Upstream culvert junction to Central Vale park reservoir (Source: Tembo, 2016)
4.3.2 Stage 2
In thisstage,ratingcurveswere constructedinorderto obtaininflows.The firststepwas
determiningthe channel sectionsurface roughnesscoefficient,whichwasbasedon‘book’values
takenfromChow(1959). Thiswas achievedthroughvisual inspection of site photographsand
runningsimulationsonFloodModellerPro(Floodmodeller.com, 2016) for a range of possible culvert
surface roughnesscoefficients.Thisissummarisedinthe Figure4-3 and Figure4-4, whichgivesa
photographicdescriptionof the culvertsurface roughnesstobe determinedanditscorresponding
culvertprofile,aspresentedonFloodModellerPro(2016).The culvertsurfacescircled1and 2 in
Figure 4-3 and itscorrespondingsectionplot shall be assignedarange of roughnesscoefficients,
extractedfromChow(1959).
Figure 4-3 Visual inspection of culvert surface roughness (Source: Tembo, 2016)
Furthermore,soundengineeringjudgment,insteadof intuitive reasoningshall be applied for
determiningthe roughnesscoefficientstobe assignedtothe culvertsurfacescircledinthe Figure4-
3. This shall be achievedbyrunningsimulationsconfiguredwiththe range of Manning’scoefficients
1
2
1
2

38
and thenselectingthe ratingcurvesthatbestfitthrougha plotof gauge pointfielddata,inorderto
ensure thatthe ratingsare sensible.Thisprocesswill be carriedoutforall the three floodevents.
4.3.3 Stage 3
Afterestablishingthe ratingcurvesforthe differentManning’s‘n’andthe three different
floodevents,the nextstepinvolvesrunningthe modelagainstdifferentstructure inletcoefficient
combinationstakenfromthe CIRIA andHydraulicDesignManual andobservingthe range of
variationinthe levelsatthe upstreamBurnleyroadculvertCVPoutlet.The inletcoefficient
combinationswere selectedtobestmatchthe photographicdescriptionof the culvertinletshownin
the Figure 4-5.
Figure 4-5 Culvert inlet (Source: Jepps, 2016)
The findingscanbe usedto provide commentaryonthe suitabilityof the inletstructure
configurationandidentifyoverestimatesof peakfloodlevelsbyusingthe CIRIA coefficients.
4.4 Data Analysis
The quantitative dataanalysiswascarriedoutusingthe hydraulicmodellingsoftware Flood
ModellerPro.The FloodModellerProinterface allowedforthe quantitative datatobe manually
codedfor inputssuchas time steps(unsteady-fixedtime step),Manning’sroughnesscoefficients,
gauge pointdata waterlevelsandculvertentrance losscoefficients(derivedfromCIRIA and
HydraulicDesignManual methodologies),whichallowedfordetailedanalysisof testreach.The
representationof statistical indicatorswasdone throughMicrosoftexcelsoftware forall the graphs
and tables.
For ease inquantitative analysis,anon-parametricdataapproachwassought andpresented
inthe formof a matrix throughwhichall the combinationswere assessedagainsteachotherandthe
outcomesof theirlevel variationswerecomparedtothe observedlevelssituatedat the CVPoutlet
for eachfloodevent. Table4-1 matrix below summarisesthisapproach.

39
CIRIA Non-CIRIA
Best
CIRIA
High
CIRIA
Low
CIRIA
Bestnon-
CIRIA
Highnon-
CIRIA
Low non-
CIRIA No loss
High
Manning's HM_BC HM_HC HM_LC HM_BNC HM_HNC HM_LNC HM_NL
Best
Manning's BM_BC BM_HC BM_LC BM_BNC BM_HNC BM_LNC BM_NL
Low
Manning's LM_BC LM_HC LM_LC LM_BNC LM_HNC LM_LNC LM_NL
Table 4-1 Manning's surface roughness and entrance loss coefficient combinations matrix (Source: Tembo, 2016)
4.5 Limitations
However,certainconcernswere identified,whenitcame toextractingthe inflows.Inflows
presentedwere basedona modelledratingcurve derivedfromupstreamlevels,ratherthanthe
actual measuredflows,whichisoftenthe case duringfloodevents,whenthe discharge inchannels
ishigh.Thismakesit difficulttomonitorthe waterlevelsandflow rateseffectively(Knight,2013).
Hence,itwas importanttoensure thatthe modelledinflowswere accurate,beforecarryingthe
analysisforward.Furthermore,thisalsomeantthatthe modelledratingwouldalsobe sensitive to
any changesmade to the model.Forinstance,anincrease inManning’s‘n’scenariowouldresultin
lowerflows.Consequently,itwasvital tobe aware of thisduringthe analysisandensure thatthe
variabilityof thismodelledratingwassatisfactory.Toovercome thisissue,the followingapproach
was adoptedː
 Plotratingsat the CVPlevel gauge forthe highManning’s,low Manning’sandbest
Manning’sscenarios.Thishelpedobservethe sensitivityanalysisof the ratingcurve to
changeson the culvertinletgeometry.
 Plotthe resultingflowhydrographsatthe same locationtogauge itssensitivityto
changesbeingmade tothe culvertinletgeometry.
If the proceduresstatedabove are successfullyimplemented,thiswouldenable the
observationof anyvariationsinthe derivedinflows.There ishowever,the potential forasubstantial
variationinlevels.Insucha case,a furtherroundof scenarioswill be carriedout,inwhichthe model
will be runas a fixedQTBDYSforeach geometryscenarioforeacheventandasubsequent
assessmentof the performance levelswill be carriedoutagainstthe observedlevels.Thiswill
provide certaintythatthe initial derivedinflowsare withinthe righttarget.

40
5 Results
5.1 Stage 1
The Figure 5-1 showsthe Stage-Time graphof the Novemberfloodevent.There isaclearindication
of the peakfloodleveloccurringonthe 15 November2015 at 09:15. The time stepsassignedtothis
eventwere between50and 110 hours as shownin Figure5-2.
Figure 5-1 12 November Upstream and Downstream level series
Figure 5-2 12 November time-steps

41
The 12 Decembereventproducedthe followingupstreamanddownstreamwaterlevels.As
shownin Figure 5-3, the peakflowoccurredon the 12 December2015 at 16:15 andthe time steps
assignedwere between0and 95 hoursas shownin Figure5-4.
Figure 5-3 12 December Upstream and Downstream level series
Figure 5-4 12 December time-steps

42
Likewise, BoxingDay eventproducedthe followingupstreamanddownstreamwaterlevels.
As shownin Figure5-5, the peakflowoccurredonthe 26 December2015 at 16:15 and the time
stepsassignedwere between 200 and 320 hoursas shownin Figure5-6.
Figure 5-5 Boxing Day Upstream and Downstream level series
Figure 5-6 Boxing Day time-steps

43
5.2 Stage 2
The range of Manning’scoefficientstobe assignedtothe culvertsurfacescanbe
summarisedinthe table5-1 below.
As perthe Manning’scoefficientsrecommendedbyChow (1959),the surface area1 was
assignedabrick descriptionwitheitheraglazedor cementmortarfinish.Surface 2was assigneda
cementdescriptionwitheitheraneatsurface or a mortarfinishanda concrete descriptionwith
eitheratrowel finishora floatfinish.
The Figures5-7, Figure5-8 and Figure5-9 below show the highManning’s‘n’,low Manning’s
‘n’and bestManning’s‘n’scenarios respectively withthe range of ratingcurvesandthe gauge point
plotsforthe BoxingDayfloodevent.
Figure 5-7 Boxing Day High Manning rating curve scenario (Source: Tembo, 2016)
127.6
127.8
128
128.2
128.4
128.6
128.8
129
129.2
129.4
0 5 10 15 20 25
Stage(m)
Flow m^3/s)
High Mannings (Boxing Day)
Gaugings
Rating v0_01
Rating v0_02
Rating v0_03
Rating v0_04
Rating v0_05
Rating v0_06
Table 5-1 Surface roughness coefficients extracted from Chow (Source: Chow, 1959)

44
Figure 5-8 Boxing Day Low Manning rating curve scenario (Source: Tembo, 2016)
Figure 5-9 Boxing Day Best Manning rating curve scenario (Source: Tembo, 2016)
The BoxingDay eventratingcurvesshownabove allowstoextractthe followingbase values:
i. HighManning’sːrating V0_06
ii. Low Manning’sːratingV0_06
iii. BestManning’sːratingV0_10
These ‘selections’canbe seentobestfitthroughthe gauge points.Therefore,the following
Figure 5-10, Figure 5-11 and Figure5-12 showsthe combinedresultsafterrunningthose base values
against12 November2015 and12 December2015 floodevents.
127.6
127.8
128
128.2
128.4
128.6
128.8
129
129.2
129.4
0 5 10 15 20 25 30
Stage(m)
Flow (m^3/s)
Low Mannings (Boxing Day)
Gaugings
Rating v0_01
Rating v0_03
Rating v0_04
Rating v0_05
Rating v0_06
Rating v0_02
127.6
127.8
128
128.2
128.4
128.6
128.8
129
129.2
129.4
0 5 10 15 20 25 30
Stage(m)
Flow(m^3/s)
Best Manning's (Boxing Day)
Gaugings
Rating v0_04
Rating v0_05
Rating v0_06
Rating v0_07
Rating v0_08
Rating v0_09
Rating v0_10

45
Figure 5-10 High Manning rating curve scenario for combined flood events (Source: Tembo, 2016)
Figure 5-11 Low Manning rating curve scenario for combined flood events (Source: Tembo, 2016)
127.6
127.8
128
128.2
128.4
128.6
128.8
129
129.2
129.4
0 5 10 15 20 25
Stage(m)
Flow(m^3/s)
HighManning's Rating Curves (All events)
Gauge points
November
December
Boxingday
127.6
127.8
128
128.2
128.4
128.6
128.8
129
129.2
129.4
0 5 10 15 20 25
Stage(m)
Flow (m^3/s)
Low Manning's Rating Curves (All events)
November
December
Boxingday
Gauge points

46
Figure 5-12 Best Manning rating curve scenario for combined flood events (Source: Tembo, 2016)
5.3 Stage 3
The culvertinletwasassignedentrance losscoefficientsdescribedwithinthe CIRIA and
HydraulicDesignManual. Table5-2 summarisesthese inletdescriptions.
CIRIA
Hydraulic Design
Manual
Inletdescription
Entrance loss
Coefficients
Inletdescription
Entrance loss
Coefficients
900
headwall/450
bevels
0.495 Headwall parallel to
embankment(no wing
walls)ːSquare-edgedon3
edges
0.5
00
headwall/top
edge
bevelled/span-
to-rise 2ː1 to 4ː1
0.61 Wingwallsparallel
(extensionofsides)ː
square-edgedatcrown
0.7
00
flared
walls/top edge
square/single
barrel (Form A)
0.005 Headwall parallel to
embankment(no wing
walls)ːRounded on 3 edges
to radius of
𝟏
𝟏𝟐
barrel
dimension,orbevelled
edgeson 3 sides
0.2
Table 5-2 Culvert inlet geometric description and corresponding entrance loss coefficients (Source: Flood Modeller Pro,
2016; Garcia, 2016)
127.6
127.8
128
128.2
128.4
128.6
128.8
129
129.2
129.4
0 5 10 15 20 25
Stage(m)
Flow (m^3/s)
Best Mannings Rating Curves (All events)
Gauge points
November
December
Boxing Day

47
The simulationswere runinFloodModellerProforthe differentManning’scoefficients
againstthe differentculvertinletgeometricdescriptionsandthe followingStage-Time relationships
were establishedforall three floodevents,asshowninthe Figure5-13, Figure5-14, Figure 5-15.
Figure 5-13 Boxing Day stage series (all combinations)
Figure 5-14 12 November stage series (all combinations)
126
126.5
127
127.5
128
128.5
129
129.5
0 200 400 600 800 1000 1200 1400 1600
Stage(m)
Time (hr)
Boxing day hydrograph
BM_BC
ʟM_ɴʟ
ʟM_ʟɴC
ʟM_ʜɴC
ʟM_BɴC
ʟM_ʟC
ʟM_ʜC
ʟM_BC
BM_ɴʟ
ʜM_ɴʟ
ʜM_ʟɴC
ʜM_ʜɴC
ʜM_BɴC
ʜM_ʟC
ʜM_ʜC
ʜM_BC
BM_HNC
BM_BNC
BM_LC
BM_HC
126
126.5
127
127.5
128
128.5
129
0 100 200 300 400 500 600 700 800
Stage(m)
Time(hr)
November hydrograph
ʜM_BC
ʟM_ɴʟ
ʟM_ʟɴC
ʟM_ʜɴC
ʟM_BɴC
ʜM_ʜC
ʟM_ʜC
ʟM_BC
BM_ɴʟ
BM_ʟɴC
BM_ʜɴC
BM_BɴC
BM_ʜɴC
BM_BɴC
BM_ʟC
BM_ʜC
BM_BC
ʜM_ɴʟ
ʜM_ʟɴC
ʜM_ʜɴC
ʜM_BɴC
ʜM_ʟC
ʟM_ʟC

48
Figure 5-15 12 December stage series (all combinations)
A site inspectionwascarriedouttoobtainactual levelsof the eventdescriptionsandverify
the anecdotal informationaforementionedinchapter4 of thisstudyfor the stage 1 procedure.The
site inspectionmeasurementsresultedinthe following:
 For BoxingDayfloodevent,the video(Appendix B) indicatedthe peaklevelsjust
overlappingthe topof the wall atthe CVPoutlet.Measurementfromthe secondstone
to the top of the copingstone were taken,asshowninthe Figure5-16 below andthe
heightof the copingstone was100 mm.This meantthat the estimatedlevelsforBoxing
Day 2016 were now128.62m.
 For 12 December2015 floodevent,the peakfloodlevel didnotoverfloodthe bank,
therefore the floodlevel thatwasassignedwas128.52m.
 For 12 November2015 floodevent,the peakfloodlevel waslow,onlyreachingtwo
stone coursesfromthe top. Therefore,the estimatedpeaklevel onthiseventwas
128.24m.
126
126.5
127
127.5
128
128.5
129
129.5
0 200 400 600 800 1000 1200
Stage(m)
Times (hr)
December hydrographs
ʜM_BC
ʟM_ɴʟ
ʟM_ʟɴC
ʟM_ʜɴC
ʟM_BɴC
ʟM_ʟC
ʟM_ʜC
ʟM_BC
BM_ɴʟ
BM_ʟɴC
BM_ʜɴC
BM_BɴC
BM_ʟC
BM_ʜC
BM_BC
ʜM_ɴʟ
ʜM_ʟɴC
ʜM_ʜɴC
ʜM_BɴC
ʜM_ʟC
ʜM_ʜC

49
The simulationsrunof FloodModellerProforthe differentManning’sandinletdescriptions
combinations producedthe followinglevel outputsshownin Table5-3, Table 5-4 andTable 5-5. The
environmentagencyallowableerrorwas+/-150mm. So,these outputscan be translatedand
expressedintermsof mmdifference,relative tothe observedi.e. CVPmodelledlevels–observed
levels.Table5-6,Table 5-7 andTable 5-8 showsthistranslation.
100mm
380mm
Figure 5-16 Coping stone height

50
Novembe
Event 128.24
CIRIA Non-CIRIA
Best
CIRIA
High
CIRIA
Low
CIRIA No loss
Best
non-
CIRIA
High
non-
CIRIA
Low
non-
CIRIA No loss
High
Manning'
s 128.072 128.466 127.206 128.181 127.966 127.995 127.918 127.88
Best
Manning'
s 128.152 128.537 128.276 127.947 128.036 128.065 127.986 127.947
Low
Manning'
s 128.346 128.714 128.446 128.42 128.203 128.234 128.153 128.113
Table 5-3 12 November modelled CVP levels
Decembe
Event 128.5
CIRIA Non-CIRIA
Best
CIRIA
High
CIRIA
Low
CIRIA No loss
Best
non-
CIRIA
High
non-
CIRIA
Low
non-
CIRIA No loss
High
Manning'
s 129.012 128.241 127.986 127.962 127.767 127.793 127.724
127.69
1
Best
Manning'
s 127.897 128.311 128.055 127.752 127.831 127.857 127.787
127.75
2
Low
Manning'
s 128.09 128.477 128.22 127.907 127.992 128.02 127.944
127.90
7
Table 5-4 12 December modelled CVP levels

51
Boxing
Day
Event 128.62
CIRIA Non-CIRIA
Best
CIRIA
High
CIRIA
Low
CIRIA No loss
Best
non-
CIRIA
High
non-
CIRIA
Low
non-
CIRIA No loss
High
Manning'
s 129.189 128.52 128.261 128.236 128.017 128.046 127.967 127.928
Best
Manning'
s 128.215 128.593 128.332 127.997 128.087 128.117 128.036 127.997
Low
Manning'
s 128.411 128.758 128.503 128.167 128.259 128.296 128.207 128.167
Table 5-5 Boxing Day modelled CVP levels
November
Event 128.24
CIRIA Non-CIRIA
Best
CIRIA
High
CIRIA
Low
CIRIA No Loss
Best
non-
CIRIA
Highnon-
CIRIA
Low
non-
CIRIA No loss
High
Manning's -0.168 0.226 -1.034 -0.059 -0.274 -0.245 -0.322 -0.36
Best
Manning's -0.088 0.297 0.036 -0.293 -0.204 -0.175 -0.254 -0.293
Low
Manning's 0.106 0.474 0.206 0.18 -0.037 -0.006 -0.087 -0.127
Table 5-6 12 November modelled CVP levels expressed in mm difference

52
December
Event
128.52
m
CIRIA Non-CIRIA
Best
CIRIA
High
CIRIA
Low
CIRIA
No
Loss
Best
non-
CIRIA
High
non-
CIRIA
Low non-
CIRIA No loss
High
Manning's 0.492 -0.279 -0.534 -0.558 -0.753 -0.727 -0.796 -0.829
Best
Manning's -0.623 -0.209 -0.465 -0.768 -0.689 -0.663 -0.733 -0.768
Low
Manning's -0.43 -0.043 -0.3 -0.613 -0.528 -0.5 -0.576 -0.613
Table 5-7 12 December modelled CVP levels expressed in mm difference
Boxing Day 128.62
CIRIA Non-CIRIA
Best
CIRIA
High
CIRIA
Low
CIRIA
No
Loss
Best
non-
CIRIA
Highnon-
CIRIA
Low non-
CIRIA No loss
High
Manning's 0.569 -0.1 -0.359
-
0.384 -0.603 -0.574 -0.653 -0.692
Best
Manning's -0.405 -0.027 -0.288
-
0.623 -0.533 -0.503 -0.584 -0.623
Low
Manning's -0.209 0.138 -0.117
-
0.453 -0.361 -0.324 -0.413 -0.453
Table 5-8 Boxing Day modelled CVP levels expressed in mm difference
Legend
<150mm difference
Between -150and +150mm
difference
>150mm difference
The followingfiguresbelowshow the variationsfromthe targetforthe differentManning,CIRIA and
Non- CIRIA inletcombinations;

53
Figure 5-17 Best CIRIA target variations for all events
Figure 5-18 High CIRIA target variations for all events
0.569
0.492
-0.168
-0.405
-0.623
-0.088
-0.209
-0.43
0.106
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Boxing Day December November
Variationfromtarget(mm)
Best CIRIA
Best Ciria, High Manning's Best Ciria, Best Manning's Best Ciria, Low Manning's
-0.1
-0.279
0.226
-0.027
-0.209
0.297
0.138
-0.043
0.474
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
High CIRIA
High Ciria, High Manning's High Ciria, Best Manning's High Ciria, Low Manning's

54
Figure 5-19 Low CIRIA target variations for all events
Figure 5-20 Best Non-CIRIA target variations for all events
-0.359
-0.534
-1.034
-0.288
-0.465
0.036
-0.117
-0.3
0.206
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
Low CIRIA
Low Ciria, High Manning's Low Ciria, Best Manning's Low Ciria, Low Manning's
-0.603
-0.753
-0.274
-0.533
-0.689
-0.204
-0.361
-0.528
-0.037
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
Best Non-CIRIA
Best Non-CIRIA, High Manning's Best Non-CIRIA, Best Manning's
Best Non-CIRIA, Low Manning's

55
Figure 5-21 High Non-CIRIA target variations for all events
Figure 5-22 Low Non-CIRIA target variations for all events
-0.574
-0.727
-0.245
-0.503
-0.663
-0.175
-0.324
-0.5
-0.006
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
Boxing Day December NovemberVariationfromtarget(mm)
High Non-CIRIA
High Non-CIRIA, High Manning's High Non-CIRIA, Best Manning's
High Non-CIRIA, Low Manning's
-0.653
-0.796
-0.322
-0.584
-0.733
-0.254
-0.413
-0.576
-0.087
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
Low Non-CIRIA
Low Non-CIRIA, High Manning's Low Non-CIRIA, Best Manning's
Low Non-CIRIA, Low Manning's

56
Figure 5-23 No Loss target variations for all events
-0.692
-0.829
-0.36
-0.623
-0.768
-0.293
-0.453
-0.613
-0.127
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
No Loss
No loss, High Manning's No loss, Best Manning's No loss, Low Manning's

57
6 Discussion
An investigationwascarriedouttotestthe suitabilityof the inletcoefficientsdescribedwithin
the CIRIA methodology.The hypothesiswasthatfornon-standardculverts,the CIRIA inlet
coefficientsare inaccurate,astheyoverestimate headlosses,whichultimatelyresultsinupstream
increasedwaterlevels.However,the datasetresultsseemstosuggest,thatthisisnotthe case as
CIRIA underestimatesandoutperformsthe non-CIRIA.
In the initial stagesof modellingthe testreach,itwasimportant to ensure thatthe inflows
beingderivedwereaccurate before theycouldbe carriedforwardforadetailedanalysis.Takinginto
account overcomingthe epistemicuncertainties,the approachwascarriedoutin orderto eliminate
any analytical biasof the derivedinflowsi.e.achievingareliableratingcurve,involvedcomparing
multiple ratingcurvesagainstasetof gauge points.The resultswere satisfactoryasthe topthree
ratingcurves,throughthe gauge pointswere extractedforBestManning’s,Low Manning’sandHigh
Manning’sas summarised intable6-1 below forthe BoxingDayevent.
Roughnesstype Modelledratingdescription Culvertsurface material
descriptionand roughness
coefficient
HighManning’s RatingV0_06 Concrete:Floatfinish –0.016
Brick: Glazed– 0.015
Low Manning’s RatingV0_06 Concrete:Floatfinish –0.013
Brick: Glazed– 0.011
BestManning’s RatingV0_10 Concrete:Floatfinish –0.015
Brick: In cementmortar –
0.015
Table 6-1 Top performing rating curves
The above roughnesscoefficientchoicesforthe BoxingDayfloodeventseemtobe
consistentinperformance whengaugedagainstthe other12 November2015 and 12 December
2015 events.Asinthe case of 12 Decemberand12 Novemberfloodevents,the ratingsappearedto
still sitwell withinthe targetgauge pointrange,whichagainreinforcedthe accuracyof the selected
Manning’sandderivedinflows.Moreover,the gauge pointsalsoallowedustoobserve towhat
degree of sensitivitythe ratingshadto anychangesin the culvertinletandManning’sroughness
coefficients.
It is worthnotingthat there ishowever,anunderlyinguncertaintywhengatheringrating
curves(andtherefore inflows) thatstemsfromthe factthat it isstill possibletoachieve abestfit
ratingcurve throughthe gauge plotpointsbyvaryingeitherthe Manning’sorthe Inletlosses
independently.Throughthe constructionof the matrix,we have beenable toreduce this
uncertaintybyvaryingboththe Manning’sandInletlosses.Inview of this,the mostsalientfinding
fromthe modelledresultswasthe trendinincreasedwaterlevelsforLow Manning’sscenariosin
boththe CIRIA andNon-CIRIA descriptionswhencomparedtothe otherscenarios.These findings
ascertainthe confidence of ourinflowsandmayalsoverywell be consistentwiththe notionthat
decreasedManning’shasaninverse relationshiptoflow rate (Sleigh,2012) andis,withthe greatest

58
certainty,justifiedinthe Flowserieschartsforall 3 floodeventsshownbelow whereagainwe see
Low Manning’sgivingoff the highestdischargeforbothCIRIA andNon-CIRIA instances.
Figure 6-1 Boxing Day Flow series for CIRIA instance
Figure 6-2 Boxing Day Flow series for Non-CIRIA instance
0
5
10
15
20
25
0 50 100 150 200 250 300 350
Flowrate(m^3/s)
Time (hr)
Boxing Day Flow - Time chart for CIRIA instance
LM_HC
HM_HC
BM_HC
0
5
10
15
20
25
0 50 100 150 200 250 300 350
Flowrate(m^3/s)
Time (hr)
Boxing Day Flow - Time chart for Non-CIRIA instance
BM_HNC
HM_HNC
LM_HNC

59
Figure 6-3 12 November Flow series for CIRIA instance
Figure 6-4 12 November Flow series for Non-CIRIA instance
0
5
10
15
20
25
0 20 40 60 80 100 120
Flowrate(m^3/s)
Time (hr)
12 November 2015 Flow-Timechart for CIRIA instance
BM_HC
HM_HC
LM_HC
0
5
10
15
20
25
0 20 40 60 80 100 120
Flowrate(m^3/s)
Time (hr)
12 November 2015 Flow-Timechart for Non-CIRIA instance
BM_HNC
HM_HNC
LM_HNC

60
Figure 6-5 12 December Flow series for CIRIA instance
Figure 6-6 12 December Flow series for Non-CIRIA instance
The resultsderivedfromthe colourcodedmatricesshowcase the CIRIA outperformingthe Non-
CIRIA inalmostall instancesandthe effectsare strongestforthe High-CIRIA scenarios.The Boxing
Day eventgives usthe greatestcertaintyaswe have the HighCIRIA as the topperformerunderall 3
combinationswiththe BestManning’sandHighCIRIA combinationshowcasingthe lowestvariation
fromthe target.Althoughthere are clearindicationsof floodlevel overestimationsnotjustforthe
12 Novembereventbutalsofor12 December(HighManning’s- BestCIRIA) andBoxingDay(High
Manning’s – Best CIRIA),the evidence isstillnotenoughtosubstantiate the researchhypothesisdue
to the lack of photographicor videorecordingevidence of the 12 November2015 and 12 December
2015 floodevents.
0
2
4
6
8
10
12
14
16
18
20
0 10 20 30 40 50 60 70 80 90 100
Flowrate(m^3/s)
Time (hr)
12 December 2015 Flow-Timechart for CIRIA instance
BM_HC
HM_HC
LM_HC
0
5
10
15
20
25
0 10 20 30 40 50 60 70 80 90 100
Flowrate(m^3/s)
Time (hr)
12 December 2015 Flow-Timechart for Non-CIRIA instance
BM_HNC
HM_HNC
LM_HNC

61
7 Conclusion
We have undertakenastudyinorderto testthe validityof the energylosscoefficients
describedwithinthe CIRIA designmanual forculvertdesign.The research carriedoutwasinspired
by the floodeventsthattookplace inNorthernEnglandduringNovember2015 to late December
2015 and wasalso aimedataddressingthe impendingneedtorectifyCIRIA’soverestimationof
energylossesthatoftenleadtoincreased waterlevels.
The study managedtoreplicate the findingsfrompreviousresearchandbuildonitbytakingan
unprecedentedapproachthroughcomparingthe performance of the CIRIA methodologyagainstthe
Texasdepartmentof transportation- Hydraulicdesignmanual.Thiscalledforthe developmentof a
hydraulicmodel onthe software FloodModellerPro(2016) underwhicha range of combinationsof
culvertinletdescriptionsandsurface roughnesscoefficientsfrombothmethodologieswere
simulated.
Our resultshave shownthatforthe CIRIA levelsobtained,there are afew instanceswhereby
the overestimationoccurshowever,thisfindingisnotenoughtosupportthe claimthat the use of
CIRIA produceshighheadlossas since outof the 3 floodevents,2were basedonanecdotal
informationaboutfloodlevelmeasurements,therefore creatingalarge window foruncertainty.
Videoevidence providedforone of the events(BoxingDay) allowedusgauge the performance of
boththe CIRIA andNon-CIRIA descriptions.Here we see the underperformance of the Non- CIRIA
wherebythe levelsfallbelowthe +/-150mmerror range setby the Environmental agencyinalmost
all combinations.Onthe otherhand,CIRIA fitsthe errorrange descriptioninalmostall eventswith
the bestperformingbeingthe BoxingDayevent.
In lightof these findings,we are confidentinthe accuracy of our derivedinflowsforthe test
reach andjudgingfromthe underperformanceof the Non-CIRIA,areasonable conclusiontothe
researchcouldbe the encourageduse of CIRIA to hydrologypractitionersovergeneral lossunits.

62
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66
9 Appendices
9.1 Appendix A – User forum
Belowisscreenshotof the FloodmodellerProuserforumlogswhere auseraddressesthe needto
rectifythe culvertinletlosses.

Testing The Validity Of Hydraulic Losses Described In The CIRIA Methodology For Culvert Design

Testing The Validity Of Hydraulic Losses Described In The CIRIA Methodology For Culvert Design

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