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A continuous simulation approach A continuous simulation approach A continuous simulation approach A continuous simulation approach

to assessing flood closures for to assessing flood closures for to assessing flood closures for to assessing flood closures for

major transport corridorsmajor transport corridorsmajor transport corridorsmajor transport corridors

Andrew Vitale

Engeny Water Management

Waterway Crossing Upgrades for Transport Waterway Crossing Upgrades for Transport Waterway Crossing Upgrades for Transport Waterway Crossing Upgrades for Transport

CorridorsCorridorsCorridorsCorridors

• Upgrade crossings to achieve consistent flood immunity standard (e.g. 10 year ARI immunity)– May not be economical for low immunity corridor

– May be better to spend money on crossings that result in longer road closures

– Need to prioritise upgrades

• Upgrade crossings with largest AAToC– Does not consider dependency between crossing closures

– Upgrading a crossing does not necessarily reduce AAToCof entire corridor if other crossings are closed at same time

• How to prioritise upgrades?

Prioritisation of Waterway Prioritisation of Waterway Prioritisation of Waterway Prioritisation of Waterway Crossing UpgradesCrossing UpgradesCrossing UpgradesCrossing Upgrades

• Depends on many factors:

– Spatial variation in rainfall along road corridor

– Variation in immunity and AAToC of individual crossings

– Closure dependency along road corridor

– Cost of crossing upgrades

– Types of road users (LV, HV)

– Availability and characteristics of alternative access routes

• Continuous simulation approach required to estimate AAToC for entire road corridor

Continuous Simulation ApproachContinuous Simulation ApproachContinuous Simulation ApproachContinuous Simulation Approach

• Model coincidental closures of individual

crossings along whole road corridor

• Can then simulate benefit of individual crossing

upgrades on overall road closure characteristics

• Economic assessment can be used to prioritise

or provide business case for crossing upgrades

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Case Study: Gore Highway Flood StudyCase Study: Gore Highway Flood StudyCase Study: Gore Highway Flood StudyCase Study: Gore Highway Flood Study

• Gore Highway connects Toowoomba and Goondiwindi

• Part of main road transport link between Brisbane and Melbourne

• Road corridor 200 km long

• Divided into 3 links for purpose of study based on alternative access routes

• Road corridor has low flood immunity (< 2 year ARI)

• Main objective of study was to develop prioritised list of waterway crossing upgrades

Gore Highway Gore Highway Gore Highway Gore Highway –––– Alternative Access RoutesAlternative Access RoutesAlternative Access RoutesAlternative Access Routes

Gore Highway Gore Highway Gore Highway Gore Highway –––– Flooding ContextFlooding ContextFlooding ContextFlooding Context Study ApproachStudy ApproachStudy ApproachStudy Approach

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Continuous Hydrology Continuous Hydrology Continuous Hydrology Continuous Hydrology –––– Catchment Catchment Catchment Catchment

DelineationDelineationDelineationDelineation

• Minimum catchment size 2 km2 (small

catchments have negligible influence on AAToC)

• Not all catchments are cross drainage (flow

parallel to road corridor can cause closures)

• Condamine River assessed through gauging

data (no hydrology modelling required)

Continuous Hydrology Continuous Hydrology Continuous Hydrology Continuous Hydrology –––– Rainfall SequencesRainfall SequencesRainfall SequencesRainfall Sequences

• Pluviometer data used to generate gridded

spatial/temporal data set of 30 min interval

rainfall totals

• Gridded data used 1 km x 1 km grid size

• Continuous rainfall data set: 1973 – 2011 (39

years)

• Sufficient period of record to assess closure

statistics for low flood immunity road corridor

Continuous Hydrology Continuous Hydrology Continuous Hydrology Continuous Hydrology –––– Rainfall SequencesRainfall SequencesRainfall SequencesRainfall Sequences Continuous Hydrology Continuous Hydrology Continuous Hydrology Continuous Hydrology –––– Flow Flow Flow Flow SequencesSequencesSequencesSequences

• Continuous flow sequences developed using

AWBM rainfall runoff routing model

• Used catchment average rainfall data set

(average of gridded data over catchment)

• AWBM parameters determined by calibration

against stream gauging data

• Catchment area based AWBM parameters used

to derive flow sequences for closure assessment

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Continuous Hydrology Continuous Hydrology Continuous Hydrology Continuous Hydrology –––– CalibrationCalibrationCalibrationCalibration

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Gauge Flow Model Flow Q5 Catchment Rainfall Intensity

Continuous Continuous Continuous Continuous HydraulicsHydraulicsHydraulicsHydraulics

• Used Flow vs Water Level rating curves at road

crossing locations from 2D flood models

• Continuous flow sequences converted to flood

level sequences using rating curves

• Allows assessment of coincident crossing

closures

Road Closure Simulation ToolRoad Closure Simulation ToolRoad Closure Simulation ToolRoad Closure Simulation Tool

• GoldSim model used to perform continuous hydrology and hydraulic simulations

• Road closure statistics calculated for each crossing, link and entire corridor:– Average Annual Time of Closure

– Average duration of closure event

– Average number of closures per year

• Adopted depth > 300 mm for closure criteria

• Tool also gives submergence statistics (D>0mm)

Road Closure StatisticsRoad Closure StatisticsRoad Closure StatisticsRoad Closure Statistics

• AAToC for Link is smaller than sum of AAToC for individual crossings

in Link – caused by coincident closures

Annual Average Time of Closure (days)

CorridorLinkCrossing - - - - - - - - 0.6 1.0 - - - - - - - - - - - - - - - - 0.1 - - 0.7 - - - 1.5 - 0.1 0.1 0.5

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Crossing ID 16

69

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50

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16

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7

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6

Westbrook - Pittsworth Pittsworth - Millmerran Millmerran - Murri Murri Plains

2.5

0 1.3 1.8

Average Duration of Closure (hr)

CorridorLink

Crossing - - - - - - - - 37.4 17.2 - - - - - - - - - - - - - - - - 11.1 - - - - - - 18.9 - 10.2 10.8 15.6

Waterway Co

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Crossing ID 16

69

8

50

53

3

16

51

34

35

0

34

35

1

25

61

2

50

60

1

50

59

1

49

73

9

24

89

9

50

68

8

50

69

1

50

72

4

50

75

3

50

75

7

50

71

4

50

75

0

50

74

9

50

74

7

50

74

2

34

34

8

34

34

9

26

24

2

26

27

3

12

85

1

22

84

6

26

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1

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7

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26

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26

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6

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10

80

7

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1

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0

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3

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Westbrook - Pittsworth

21.50 22.3 21.2

Millmerran - Murri Murri PlainsPittsworth - Millmerran

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Crossing Upgrade AssessmentCrossing Upgrade AssessmentCrossing Upgrade AssessmentCrossing Upgrade Assessment

• Road Closure Simulation Tool used to determine the Link AAToCthat remains if a particular crossing is upgraded to mitigate closure

Significant reduction in Link AAToC

Only minor reduction in Link AAToC

Rapid Economic AppraisalRapid Economic AppraisalRapid Economic AppraisalRapid Economic Appraisal

Crossing Upgrade PrioritisationCrossing Upgrade PrioritisationCrossing Upgrade PrioritisationCrossing Upgrade Prioritisation

Positive NPV

Other upgrades are

marginal when

considered in isolation

ConclusionsConclusionsConclusionsConclusions

• Benefits of approach:– Fast and low cost (derivation of rating curves using

hydraulic models is most time consuming component)

– Takes into account coincident road closures along corridor

– Allows rapid prioritisation of crossing upgrades

• Drawbacks in approach:– Generally limited to 30-40 years of pluviograph data

– Accuracy of closure statistics may be affected for high flood immunity road corridors

– Does not consider likelihood of coincident road closures along alternative routes or adjacent sections of corridor