Undertaking national flood risk assessment in England, United Kingdom Jonathan Simm

Transcription

1 Undertaking national flood risk assessment in England, United Kingdom Jonathan Simm November 18th, 2015 Presentation to AWRA conference, Denver CO

2 Overview UK background Overview of method and description of model components (including comparison with FEMA RiskMAP approach) Model outputs, uses and case study applications November 18th, 2015 England national flood risk analysis Page 2

3 UK background November 18th, 2015 England national flood risk analysis Page 3

4 Where does England fit in conceptually Colorado land area 104,000 miles 2 Land area USA Great Britain England only 3,806,000 89,000 50,000 miles 2 miles 2 miles 2 100% 2.3% 1.3% Coastline length Population Colorado 5.5 million Population England 53.0 million i.e. 10 x population in 50% land area! USA 95,500 miles Great Britain 19,500 miles. 100% 20% 6% England only 5,600 miles November 18th, 2015 England national flood risk analysis Page 4

5 England: no water supply problems (yet) Present day 2030 projection November 18th, 2015 England national flood risk analysis Page 5

6 But it does have a problem with flooding % of land in flood plain % of development in flood plain November 18th, 2015 England national flood risk analysis Page 6

7 Background UK has a long history of flooding, especially over the last 20 years, with major flood events in /14 November 18th, 2015 England national flood risk analysis Page 7

8 Example storm track 3rd January 2014 NOAA 20th Century meteorological Reanalysis November 18th, 2015 England national flood risk analysis Page 8

9 Background UK has a long history of flooding, especially over the last 20 years, with major flood events in /14 In 2002, UK government moved from flood defence towards flood risk management: To manage flood risk there is a need to quantify it. November 18th, 2015 England national flood risk analysis Page 9

10 National Flood Risk Analysis (NaFRA) National model run NaFRA 2004 NaFRA 2006 NaFRA 2008 SoN NaFRA 2005 NaFRA 2007 NaFRA 2011 Method/Software development November 18th, 2015 England national flood risk analysis Page 10

11 Flood risk analysis underpins Environment Agency s public flood maps Requirement under EU Floods Directive to produce flood risk maps and make them available to public For this purpose, information is expressed in high, medium and low flood risk bands November 18th, 2015 England national flood risk analysis Page 11

12 Analysis supports UK planning and policy Environment Agency s Long Term Investment Strategy informing 2 national comprehensive spending reviews Government contingency planning and advice to Association of British Insurers Futures work: Foresight Future Flooding analysis First UK Climate Change Risk Assessment Ongoing work for Adaptation Committee on Climate Change Local authority planning depts November 18th, 2015 England national flood risk analysis Page 12

13 Overview Overview of method and description of model components (including comparison with FEMA RiskMAP approach) November 18th, 2015 England national flood risk analysis Page 13

14 UK risk analysis approach (addresses both probability components) NFIP omits FFFFFFFFFF rrrrrrrr = PPPPPPPPPPPPPPPPPPPPPP LLLLLLLL PPPPPPPPPPPPPPPPPPPPPP (BBBBBBBBBBB aaaaaa oooo oooooooooooooooooooooo) CCCCCCCCCCCCCCCCCCCCCC $ November 18th, 2015 England national flood risk analysis Page 14

15 Sources: Extreme value analysis Water level (m) NFIP focus: return periods of 100 yr (plus 10, 50 and 500yr) UK approach: 40 return periods between 1 and 1000yrs Return period (years) Data requirements: River flows / levels; coastal water levels and wave conditions Note: All data and models are owned by the Environment Agency (EA) and publicly available. However, EA analysis outcomes are rarely appealed Insurance private impacts land-use. November 18th, 2015 England national flood risk analysis Page 15

16 Sources: 2015 upgraded estimate of coastal forcing 1) Multivariate extreme value analysis 2) SWAN wave model emulator 3) Surfzone model 4) BAYONET overtopping model November 18th, 2015 England national flood risk analysis Page 16

17 Pathways: Assessment of levee failure probability Probability of failure Probability X(m) Freeboard Water level load Not required under FEMA Structural-based Inundation Procedure (SIP) UK approach uses fragility curves to assess Breach simulation November 18th, 2015 England national flood risk analysis Page 17

18 Developing fragility curves: the RELIABLE tool Structure-specific parameters, probability distribution functions and ranges Numerical Integration Structure-specific Fault tree Limit state equation Failure mode 1 Limit state equation Failure mode 2 Limit state equation Failure mode 3 Structure-specific fragility curve Limit state equation Failure mode..n Tool available at November 18th, 2015 England national flood risk analysis Page 18

19 Site specific fragility curve November 18th, 2015 England national flood risk analysis Page 19

20 Reliability of levees generic fragility curves Over 60 generic levee types Generic curves provide an economic approach to implementing BW12/NAS P (breaching feeboard) Condition grade1 Condition grade2 Condition grade 3 Condition grade4 Condition grade Overflow head (Water level - crest level) November 18th, 2015 England national flood risk analysis Page 20

21 Breach simulation Breach simulation defines breach dimensions: levee doesn t vanish if failure occurs (Applicable to LAMP) November 18th, 2015 England national flood risk analysis Page 21

22 Breach tools developed by HR Wallingford (now working with DSIG and USACE ERDC) Erodible top layer Resistant top layer November 18th, 2015 England national flood risk analysis Page 22

23 All levees but with variable influence LAMP is applied only to non-accredited levees, whereas UK process is applied to all levees using a whole system approach NFIP process involves a binary (in/out) influence of levees.uk process is graduated November 18th, 2015 England national flood risk analysis Page 23

24 Pathways: Flood inundation analysis Current FEMA process: independent reach-specific inundation UK process: integrated across all reaches Analysis includes: (1) 40 return periods between 1 and 1000 years return period. (2) For defended flood plains for each return period, a Monte Carlo analysis is required with multiple realisations of system state (levee segments failed or not failed) (3) Analysis also covers each return period for undefended floodplains November 18th, 2015 England national flood risk analysis Page 24

25 Pathways: Flood inundation Data requirements: Digital terrain model Range of hydrodynamic models: Volume based Rapid Flood Spreading Model (RFSM) Diffusion wave (Dynamic RFSM) Hybrid models (local acceleration with sub-grid topography, RFSM EDA) Full Shallow Water Equations e.g. InfoWorks RS & CS, TELEMAC, Tuflow, etc For repeated analyses in Monte Carlo simulations, models must run very fast November 18th, 2015 England national flood risk analysis Page 25

26 Receptors: Consequences Once water depths are calculated the approach is similar to HAZUS Data requirements: Property types and locations; Depth/Damage ($) relationships Depth Damage Curve Depth Metres High Susceptibility Band Low Susceptibility Band Indicative Susceptibility Damage /m2 November 18th, 2015 England national flood risk analysis Page 26

27 Receptors: Consequences Both UK and FEMA (HAZUS) approaches are similar. (More individual calculations in UK case) Data requirements: Property types and locations; Depth/Damage ($) relationships Depth Damage Curve Depth Metres High Susceptibility Band Low Susceptibility Band Indicative Susceptibility Damage /m2 November 18th, 2015 England national flood risk analysis Page 27

28 Model outputs, and case study applications November 18th, 2015 England national flood risk analysis Page 28

29 Likelihood of flooding November 18th, 2015 England national flood risk analysis Page 29 Page 29

30 Risk EAD ( K) November 18th, 2015 England national flood risk analysis Page 30

31 Risk attribution to levee segments supports risk mitigation by structural interventions November 18th, 2015 England national flood risk analysis Page 31

32 Managing flood risk Levees only one solution: All changes and interventions can be expressed in probabilityconsequence space (Adapted from Sayers et al, 2003) November 18th, 2015 England national flood risk analysis Page 32

33 Managing changing flood risk system (Evans, et al, 2008) November 18th, 2015 England national flood risk analysis Page 33

34 Likelihood of flooding November 18th, 2015 England national flood risk analysis Page 34 Page 34

35 2100 High Emission Scenario Likelihood of flooding: sea level rise to th July 2014 CliMathNet Extremes Meeting

36 Summary and conclusions UK and US face similar flooding problems and analysis methods use the same underlying principles The ability to communicate risk and potential solutions to decision-makers is critical Full system flood risk analysis enables spatial variation in risk to be evaluated, including residual risk attributable to levees A wide range of flood risk management actions/decisions can be supported by the UK style of risk modelling presented November 18th, 2015 England national flood risk analysis Page 36

37 Undertaking national flood risk assessment in England, United Kingdom Jonathan Simm November 18th, 2015 Presentation to AWRA conference, Denver CO