New design rainfalls Janice Green, Project Director IFD Revision Project, Bureau of Meteorology
Design Rainfalls
Design Rainfalls Severe weather thresholds Flood forecasting assessing probability of rainfalls Assigning probability to observed rainfalls
Design Rainfalls New probability terminology adopted by Engineers Australia for ARR2016
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 ARR2016 http://book.arr.org.au/ 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 12 6 99.75 1.002 0.17 4 98.17 1.02 0.25 3 95.02 1.05 0.33 WSUD 2 86.47 1.16 0.50 Frequent Infrequent Rare Extremely Rare 1 63.21 1.58 1.00 0.69 50.00 2 1.44 Stormwater/pit and pipe 0.5 39.35 2.54 2.00 design 0.22 20.00 5 4.48 0.2 18.13 5.52 5.00 0.11 10.00 10 10.00 0.05 5.00 20 20.00 0.02 2.00 50 50.00 0.01 1.00 100 100.00 0.005 0.50 200 200.00 Floodplain Management 0.002 0.20 500 500.00 0.001 0.10 1000 1000.0 0.0005 0.05 2000 2000.0 0.0002 0.02 5000 5000.0..... PMP/ PMPDF Design of high consequence infrastructure (eg. Major dams)
Design Rainfalls
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
Frequent & infrequent design rainfalls (IFDs)
Frequent & Infrequent Design Rainfalls (IFDs) IFDs
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
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
Greatly expanded database
Greatly expanded database
'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
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
New IFDs
New IFDs
New IFDs
Differences between new & old IFDs
Differences between new & old IFDs
Differences between new & old IFDs
Design Rainfalls Severe weather thresholds Flood forecasting assessing probability of rainfalls Assigning probability to observed rainfalls
Severe Weather Determining thresholds used for issuing warnings for rainfalls that are conducive to flash flooding Labelling forecast rainfall as heavy
New South Wales
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.
Observed storms Assigning probability to observed rainfalls Comparing observed storms to IFDs Uses the Australian Integrated Forecasting System (AIFS)
Very frequent design rainfalls
Very Frequent Design Rainfalls
Very frequent design rainfalls Probabilities > 1EY Estimates not previously provided Limited information available on very frequent design rainfalls EY AEP (%) ARI (years) ARI (months) 12 99.99 0.08 1 month 6 99.75 0.17 2 month 4 98.17 0.25 3 month 3 95.02 0.33 4 month 2 86.47 0.50 6 month 1 63.21 1.00 12 month
Very frequent design rainfalls
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
Very frequent design rainfalls Data New IFDs Very frequent Number of rainfall stations Daily-read: 8074 Continuous: 2280 Daily-read: 15 364 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!!
Very frequent design rainfalls
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
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
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 2013 3 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 0.42 0.40 0.38 0.5 x Q 1year (flow) 0.41 0.40 0.38 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 > 0.30 0.37 0.37 0.36 Majority of state < 0.45 Ratio 4EY to 1EY 3 day
Rare design rainfalls
Rare Design Rainfalls (IFDs)
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
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
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
Summary
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)
Thank you Questions? Email: ifdrevision@bom.gov.au