A continuous simulation approach to assessing flood closures for major transport corridors

Transcription

1 12/7/217 A continuous simulation approach to assessing flood closures for major transport corridors Andrew Vitale Engeny Water Management Waterway Crossing Upgrades for Transport Corridors Upgrade crossings to achieve consistent flood immunity standard (e.g. 1 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 AAToC of entire corridor if other crossings are closed at same time How to prioritise upgrades? Prioritisation of Waterway Crossing 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 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 1

2 12/7/217 Case Study: Gore Highway Flood Study Gore Highway Alternative Access Routes Gore Highway connects Toowoomba and Goondiwindi Part of main road transport link between Brisbane and Melbourne Road corridor 2 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 Flooding Context Study Approach 2

3 12/7/217 Continuous Hydrology Catchment Delineation Minimum catchment size 2 km 2 (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 Rainfall Sequences Pluviometer data used to generate gridded spatial/temporal data set of 3 min interval rainfall totals Gridded data used 1 km x 1 km grid size Continuous rainfall data set: (39 years) Sufficient period of record to assess closure statistics for low flood immunity road corridor Continuous Hydrology Rainfall Sequences Continuous Hydrology Flow Sequences 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 3

4 12/7/217 Continuous Hydrology Calibration Continuous Hydraulics F lo w (m 3 /s ) Catch m en t Rainfall (m m /hr) F lo w ( m 3 /s ) C a tch m e n t R a in fa ll ( m m /h r ) 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 Jan 19 Jan 23 Jan 27 Jan 31 Feb 4 Feb 8 Feb Jan 2 Jan 3 Jan 4 Jan 5 Jan 6 Jan 7 Jan 8 Jan 9 Jan 1 Jan 11 Jan 12 Jan 13 Jan 14 Jan 15 Date Date Gauge Flow Model Flow Q5 Catchment Rainfall Intensity Gauge Flow Model Flow Q5 Catchment Rainfall Intensity Road 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 > 3 mm for closure criteria Tool also gives submergence statistics (D>mm) Road Closure Statistics Crossing Annual Average Time of Closure (days) Westbrook - Pittsworth Pittsworth - Millmerran Millmerran - Murri Murri Plains Corridor 2.5 Link Waterway Crossing ID Average Duration of Closure (hr) Corridor Link Condamine River Back Creek Crossing Waterway Crossing ID Westbrook - Pittsworth Pittsworth - Millmerran Millmerran - Murri Murri Plains Condamine River Back Creek AAToC for Link is smaller than sum of AAToC for individual crossings in Link caused by coincident closures Yarrill Creek 26351_P Yarrill Creek 26351_P 26351_CD 26351_CD Tributary Commorron Creek Floodplain Tributary Commorron Creek Floodplain Comorron Creek 186 Comorron Creek 186 4

5 12/7/217 Crossing Upgrade Assessment Rapid Economic Appraisal Road Closure Simulation Tool used to determine the Link AAToC that remains if a particular crossing is upgraded to mitigate closure Only minor reduction in Link AAToC Significant reduction in Link AAToC Crossing Upgrade Prioritisation Positive NPV Other upgrades are marginal when considered in isolation Conclusions 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 3-4 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 5