New design rainfalls. Janice Green, Project Director IFD Revision Project, Bureau of Meteorology

Transcription

1 New design rainfalls Janice Green, Project Director IFD Revision Project, Bureau of Meteorology

2 Design Rainfalls

3 Design Rainfalls Severe weather thresholds Flood forecasting assessing probability of rainfalls Assigning probability to observed rainfalls

4 Design Rainfalls New probability terminology adopted by Engineers Australia for ARR2016

5 New Probability Terminology Being adopted by Engineers Australia for ARR2016 Objectives are: Clarity of meaning Technical correctness Practicality and acceptance Details available in Book 1; Chapter 2 of ARR Moving away from ARI Adopting: Annual Exceedance Probability Exceedances Per Year Frequency AEP ARI Typical Use Descriptor EY AEP (%) (1 in x) (Years) Very Frequent WSUD Frequent Infrequent Rare Extremely Rare Stormwater/pit and pipe design Floodplain Management PMP/ PMPDF Design of high consequence infrastructure (eg. Major dams)

6 Design Rainfalls

7 Design Rainfall Project ARR Revision Project 1 Phase 1 Frequent & infrequent (IFDs) Released 1 July 2013 Phase 2 Very frequent Rare To be released in 2016 Bureau contribution ~ 50 person years ~$6 million Phase 2 IFDs Phase 1 Phase 2

8 Frequent & infrequent design rainfalls (IFDs)

9 Frequent & Infrequent Design Rainfalls (IFDs) IFDs

10 Previous IFDs 1987 Australian Rainfall & Runoff Developed nearly 30 years ago Bureau's daily read & pluviograph stations Techniques appropriate at the time Focus on structures in large rural catchments Durations less than 5 minutes not provided Climate change not considered

11 Greatly expanded database Data New IFDs ARR87 IFDs Number of rainfall stations Daily-read: 8074 Continuous: 2280 Daily-read: 7500 Continuous: 600 Period of record Up to December 2012 Up to ~1983 Length of record used in analyses Source of data Quality controlling Daily-read: > 30 years Continuous: > 8 years Organisations collecting rainfall data across Australia Automated and manual Daily-read: > 30 years Continuous: > 6 years Bureau of Meteorology (primarily) Manual

12 Greatly expanded database

13 Greatly expanded database

14 'State of the science methods' Step New IFDs ARR87 IFDs Extreme value series Annual Maximum Series Annual Maximum Series Frequency analysis Extension of sub-daily rainfall statistics to daily-read stations Gridding Generalised Extreme Value distribution fitted using L-moments Bayesian Generalised Least Squares Regression Objective; automated gridding procedure using ANUSPLIN Log-Pearson Type III distribution fitted using method of moments Principal Component Analysis Maps hand-drawn

15 New IFDs Released 1 July 2013 Standard durations of: 1, 2, 3, 4, 5, 10, 15, 30 minutes 1, 2, 3, 6, 12 hours 1, 2, 3, 4, 5, 6, 7 days Standard probabilities of: 1EY (1 exceedance per year) 50%, 20%, 10%, 5%, 2%, 1% AEP Available via web includes lots of information

16 New IFDs

17 New IFDs

18 New IFDs

19 Differences between new & old IFDs

20 Differences between new & old IFDs

21 Differences between new & old IFDs

22 Design Rainfalls Severe weather thresholds Flood forecasting assessing probability of rainfalls Assigning probability to observed rainfalls

23 Severe Weather Determining thresholds used for issuing warnings for rainfalls that are conducive to flash flooding Labelling forecast rainfall as heavy

24 New South Wales

25 Flood forecasting HyFS enables forecasters to view the AEP of observed rainfall in real time Forecaster selects duration If 20% AEP threshold crossed, AEP is shown next to the observed rainfall amount in the spatial display. Provides forecaster with situational awareness and provides historical context to observed rainfall Proved very beneficial to operational forecasters - when see an AEP shown are quickly aware of heavy rainfall and potentially a significant flood. Examples from the recent flooding along the East Coast of NSW.

26 Observed storms Assigning probability to observed rainfalls Comparing observed storms to IFDs Uses the Australian Integrated Forecasting System (AIFS)

27 Very frequent design rainfalls

28 Very Frequent Design Rainfalls

29 Very frequent design rainfalls Probabilities > 1EY Estimates not previously provided Limited information available on very frequent design rainfalls EY AEP (%) ARI (years) ARI (months) month month month month month month

30 Very frequent design rainfalls

31 Very frequent design rainfalls Source WSUD Guideline Method Hastings Council Stormwater Management Design Storm equivalent to a 3 month ARI storm event 40% of 1 year ARI storm event Parramatta City Council Stormwater Asset Plan 3 month ARI storm event 0.5 x Q 1year (flow) South Australia Government 3 month design flows Logarithmic extrapolation of design flows from AR&R87 NSW State Government Stormwater Source Control 3 month ARI rainfall event 25% x 1 year ARI (rainfall) Gold Coast City Council Queensland Urban Drainage Manual 2013 Factors applied to 1 in 1 year ARI 0.5 x 63%AEP (1 in 1 year) to replace 3 month ARI terminology 3 month ARI = 0.50 x 1:1 year ARI 0.5 x 63% AEP

32 Very frequent design rainfalls Data New IFDs Very frequent Number of rainfall stations Daily-read: 8074 Continuous: 2280 Daily-read: Continuous: 2722 Period of record Up to December 2012 Up to December 2012 Length of record used in analyses Source of data Quality controlling Daily-read: > 30 years Continuous: > 8 years Organisations collecting rainfall data across Australia Automated and manual Daily-read: > 5 years Continuous: > 5 years Organisations collecting rainfall data across Australia More!!

33 Very frequent design rainfalls

34 Very frequent design rainfalls Step New IFDs Very frequent Extreme value series Annual Maximum Series Partial duration series Frequency analysis Extension of sub-daily rainfall statistics to daily-read stations Gridding Generalised Extreme Value distribution fitted using L-moments Bayesian Generalised Least Squares Regression Objective; automated gridding procedure using ANUSPLIN Generalised Pareto (GPA) distribution fitted using L-moments Ratios Objective; automated gridding procedure using ANUSPLIN

35 Very frequent design rainfalls To be released in 2016 Standard durations of: 1, 2, 3, 4, 5, 10, 15, 30 minutes 1, 2, 3, 6, 12 hours 1, 2, 3, 4, 5, 6, 7 days Standard probabilities of: 2, 3, 4, 6 and 12 EY Will be available via web

36 Very frequent design rainfalls Source WSUD Guideline Method Design Storm equivalent to a 3 month ARI storm event Hastings Council Stormwater Management Parramatta City Council Stormwater Asset Plan South Australia Government NSW State Government Stormwater Source Control Gold Coast City Council Queensland Urban Drainage Manual month ARI storm event 3 month design flows 3 month ARI rainfall event Factors applied to 1 in 1 year ARI 0.5 x 63%AEP (1 in 1 year) to replace 3 month ARI terminology 40% of 1 year ARI storm event Ratio 4EY to 1EY 1 day Ratio 4EY to 1EY 2 day x Q 1year (flow) Logarithmic extrapolation of design flows from AR&R87 25% x 1 year ARI (rainfall) 3 month ARI = 0.50 x 1:1 year ARI 0.5 x 63% AEP NA NA NA Majority of state > Majority of state < 0.45 Ratio 4EY to 1EY 3 day

37 Rare design rainfalls

38 Rare Design Rainfalls (IFDs)

39 Rare Design Rainfalls Used for the design of bridges Undertaking spillway adequacy assessments Screening analysis in Interim Climate Change Guideline 1 in 100 AEP => 1 in 200 AEP; 1 in 500 AEP

40 Rare design rainfalls CRC-FORGE method provided design rainfalls for: Durations of 1, 2, 3, 4, and 5 days AEPs of 1 in 50; 100; 200; 500; 1000 and 2000 CRC-FORGE applied to each state & territory with exception of parts of Northern Territory

41 Rare design rainfalls To be released in 2016 Standard durations of: 1, 2, 3, 4, 5, 6, 7 days Standard probabilities of: 1 in 100; 1 in 200; 1 in 500; 1 in 1000; 1 in 2000 AEP Will be available via web

42 Summary

43 New design rainfall product Standard durations of: 1, 2, 3, 4, 5, 6, and 7 days Standard probabilities of: 12EY to 1 in 2000 AEP Available for whole of Australia Derived using consistent Database Methods Available from Bureau's website Provides 'one stop shop' To be released in 2016 (New IFDs available now, however possible changes to 2% and 1% AEP)

44 Thank you Questions?