Integrated flood modelling and mitigation analysis 8 th Australasian Natural Hazards Management Conference (ANHMC2015)

Transcription

1 Integrated flood modelling and mitigation analysis 8 th Australasian Natural Hazards Management Conference (ANHMC2015) Raymond Cohen Mahesh Prakash James Hilton Yunze Wang Fletcher Woolard 3:45-4:15pm Wednesday 14 October

2 Background

3 Motivations Australian councils are required to manage risk associated with areas that are prone to flooding from storm surge, heavy rainfall and catchment flooding Simultaneous combinations of these events are especially challenging Step 1: Identify present and future flood risk Computational simulations of worst case conditions now and in the future Make land use and planning decisions based on these results Step 2: Propose mitigation strategies to reduce impact of flood events Use computational modelling to determine delivered benefits of each strategy Evaluate cost/benefit options Make informed decisions for how to optimally allocate funds Could just be one option over another Attack / defend / withdraw

4 Swift Hydrodynamic Model Water depth << width 2D formulation Predicts water height, momentum Shallow water finite volume model depth width Dam breaks Flash flooding Coastal inundation

5 Swift Hydraulic Model Pressure head-based pipe network model Assume sound speed >> gravity wave speed Pipe network both helps and hinders flooding: Normal conditions: Drainage reversal: Drainage flow direction = Drainage flow direction = Storm tide

6 Swift Flood Modelling Framework Integrated hydrodynamic/hydraulic flood modelling Modular & flexible Very fast - GPU accelerated code Capable of investigating storm surge, extreme rainfall, catchment flooding, sea level rise Able to study mitigation options in an integrated manner Developing software front end C-FAST aimed specifically for Australian councils and to be used by council engineers

7 Case studies CSIRO been involved in a number of flood modelling studies Today we will discuss: City of Port Phillip Shire of Murray City of Bunbury (current)

8 City of Port Phillip (CoPP)

9 Port Phillip Bay and CoPP CoPP Largest embayment in the world CoPP is one of 10 cities around the bay Legacy of engineering problems

10 CoPP 100,000 residents and over 22,000 businesses. Population likely to double in next years due to development at Fishermans Bend Elwood Swamp 1886 Structural mitigation options: Levees, basins and dams Drainage networks

11 Project goals From a practical engineering or on-ground management perspective, want to understand what combinations of mitigation solutions work: Adaptation type (examples) Upstream retention/ detention & diversion pipes On-lot retention/detention Mitigates what type(s) of flooding? For what period? At what cost??????? Offshore reef??? Back valves???

12 Model inputs Council wide terrain and bathymetry (LiDAR) Hydraulic and Hydrological (eg. drainage network) Storm surge with a peak of 1.3 m 1 in a 100 ARI rainfall for 3 hrs (also 1 in 5 and 1 in 10 ARI) Total simulation time = 24 hrs Rainfall starts at peak storm surge No upstream storm water reception (except in main drains) Sea level rise (SLR) = current day, 0.4, 0.8 and 1.1 m

13 Hydrodynamic Model City of Port Phillip Extensive urban drainage network (~13k pipes) Model effects of 1.3 m storm surge Flow reversal back up the drainage network is critical feature to model for CoPP 0.1 m 3 /s Flow rate 0 m 3 /s N

14 Flood visualisation current day

15 Flood summary current day Areas affected Elwood, Middle Park, Beacon Cove, South Melbourne Flood type mostly nuisance (0 to 0.3 m for less than 1 hr) except small sections around Elwood and South Melbourne Retention time

16 Flood visualisation SLR 1.1 m

17 Flood summary current day Areas affected Elwood, Middle Park, Beacon Cove, South Melbourne Flood type severe flooding in all parts affected including very alarming long lived flooding (> 12 hrs+) around most parts of Elwood canal, South Melbourne and Middle Park Retention time

18 Mitigation options applied

19 Mitigation summary SLR 0.0 m (current day) Without mitigation With mitigation Retention time Focus area Elwood canal Mitigation achieved Flooding at intersection of Barkly and Meredith street completely stopped

20 Shire of Murray (SoM)

21 SoM Project Murray (and Serpentine) river delta Series of eight low lying islands and coastal areas At the confluence of two rivers (the Murray and the Serpentine) where they flow into the Peel estuary in South Yunderup WA Areas of cultural, heritage and future infrastructure value A combination of several factors puts the delta at high risk, including Sea level rise Increased frequency and severity of storm surges Greater tidal influence and salinity Poorly planned protection measures

22 SoM topography and bathymetry

23 SoM simulation cases Case Sea level Simulation description (above 2014 AHD) m Current day with storm surge m 2030 with storm surge m 2070 with storm surge m 2100 with storm surge

24 SLR 0.0 m SLR 0.14 m SLR 0.4 m SLR 0.8 m

25 SLR 0.0 m SLR 0.14 m SLR 0.4 m SLR 0.8 m

26 Findings Heritage listed Mill on the western Tip of Culeenup SLR 0.0 m - only nuisance flooding SLR 0.14 m - significantly flooded m persisting for 8+ hours Money would be better spent protecting the Mill prior to investing in restoration Homes in the Murray Delta in the three inhabited islands SLR 0.0 m, 0.14 m - inundation minimal SLR 0.4 m - 40% homes inundated SLR 0.8 m - whole of Yunderup Island is inundated Mitigation options prove ineffective from a cost/benefit perspective due to the scale and extent of flooding. Might be some benefit in investigating basic mitigation such as a levee or barrier perhaps for Yunderup Island where the extent of flooding is less dramatic

27 City of Bunbury (CoB)

28 CoB Flood mitigation analysis City of Bunbury (CoB) is a developing low-lying coastal region especially susceptible to flooding from combined storm surge and rainfall events Areas around the Preston River and the Leschenault Inlet historically worst hit WA-NDRP project to study flooding for future planning needs and to assess mitigation options Investigation into extreme present and future (with SLR) flooding events and the impact of potential mitigations including Retention/detention schemes Changes to the drainage network e.g. back valves, additional pipes Changes to pumping stations Sea walls

29 Data collection Input data types Lidar, bathymetry, land usage Drainage network, pumps Rainfall Tides Joint probability analysis Statistical extreme tide & rainfall scenarios

30 Scenarios to be considered A. Extreme rainfall into 5 Mile Brook sub-catchment B. Storm surge into northern Bunbury C. Preston River response to heavy rainfall

31 A. Extreme rainfall Five Mile Brook sub-catchment Issue: Extreme rainfall from new Dalyellup development will drain into Five Mile Brook. Impact on Bunbury pipe network is unknown. Mitigation option Prescribe maximum inflow allowance

32 B. Storm surge Impact on northern Bunbury Issue: Storm surge and SLR has the capacity to overtop Koombana Drive and to flood Leschenault Inlet / northern Bunbury Mitigation options New sea wall Permanently close storm surge barrier and lower water level of Leshenault Inlet

33 C. Preston river Response to heavy rainfall Issue Low lying housing along the Preston River are susceptible to flooding from extreme rainfall / levee bank failure Mitigations More accurately define the potential flood plain Improve levee banks Redirect river course into the Leschenault Inlet

34 Future directions

35 Swift CSIRO is developing a tool C-FAST based on Swift which can model urban flooding A number of case studies have been undertaken which have provided detailed requirements from a diverse range of councils across Australia In the next 18 months the intention is to deploy the tool for use internally by the early adopter councils we have already worked with Council engineers will be empowered to run new simulations with incrementally updated input data and to rapidly experiment with proposed mitigation options

36 Thank you Computational Modelling & Simulation Dr. Raymond Cohen Research Scientist t e Raymond.Cohen@csiro.au w