1. The revision of Australian Rainfall and Runoff: implications for floodplain managers Tony Ladson

2. 1958 1977 1987 19 10 ~30

3. Benefits of adoption Greater accuracy Better justification Improved guidance

4. What engineers learn at University Techniques engineers apply ARR Influences Updating ARR will improve training and practice

5. Consultant to CMA “Please specify the methods we should use in this flood study” Brain surgeon to patient “Please specify the surgical methods I should use”

6. Onus is on practitioners to stay up to date National Committee on Water Engineering “…the responsibility [is] on practitioners to stay abreast of current research/best practice and not to use out-dated techniques even when documented in ARR 1987” “ARR is not to be treated as a standard where compliance with the published document constitutes acceptable practice”

7. CMA Head Office ARR Influences The Brief The Results

8. Updating ARR will influence assessment of: Design flood magnitude –Flood frequency –Rainfall intensity –Rational method

9. Flood Frequency Update ARR 1987 Flood flow ARR 2015 1% year flood

10. Flood Frequency Draft chapter has been available since 2006 Web-based software –http://www.tuflow.com/flike.aspx

11. IFD update (Project 1) 100-year, 1 hour rainfall for Mildura: 47 mm – 1987 56.4 mm – 2013 An increase of 20%

12. 1 Year2 years5 years10 years20 years50 years100 years 5Mins -2%-11%1%10%14%20%26% 10Mins -1%-10%2%11%15%22%27% 30Mins -7%-15%-3%6%10%17%23% 1Hr -10%-18%-7%3%7%14%20% 2Hrs -9%-18%-7%2%6%13%18% 3Hrs -8%-17%-7%2%5%12%17% 6Hrs -3%-14%-5%2%5%10%15% 12Hrs 1%-11%-5%1%3%6%9% 24Hrs 1%-11%-6%-1%0%1%3% 48Hrs -1%-13%-8%-3% -2% 72Hrs 0%-12%-7%-3%

13. IFD % change

14. What was the 1:100 year 5 min or 10 min storm now occurs with a frequency of about 40 years

15. Rational Method update Rural Rational Method to be replaced by a regional method (Project 5) Urban Rational Method (Project 13)

16. If we change the design flood magnitudes then modelled flood extents will change

18. Updating ARR will influence assessment of: Design flood magnitude Flood hazard

19. Flood Hazard

21. ARR Project 10 –Safety criteria for people –Safety criteria for vehicles

24. Flood Hazard: many other sources of information in addition to ARR SCARM (2000) Floodplain management EMA (1999) Managing the floodplain Melbourne Water (2003) NSW Floodplain Development Manual NFRIP (National Flood Risk Information Project) National Flood Guidelines, Managing the Floodplain

26. Updating ARR will influence assessment of: Design flood magnitude Flood hazard Terminology

27. Flood terminology Not the 100-year flood –1% flood Not the 3 month flood –Flood with 4 exceedances per year

28. ARR update process ~ 20 to 30 projects and other products Funded by the Commonwealth Government Managed by Engineers Australia Editor: James Ball Dr Rory Nathan is on the Technical Committee Dr Andrew McCowan is actively involved

29. Status of key projects 23 technical “projects” –3 draft chapters (13%) –5 useable outputs (22%) –6 in progress (26%) –6 no outputs (26%) –3 not funded (13%)

30. Draft chapters –Flood Frequency Analysis –Baseflow estimation for modelling (P7) –Safety/Hazard (P10)

31. Usable –IFD (Project 1) –Spatial patterns of rainfall (P2) –Blockage (P11) –2D models (P15) –Monte Carlo approaches in hydrology

32. In progress –Continuous rainfall (P4) –Regional flood methods (P5) –Losses for flood modelling (P6) –Rational method (P13) –Coastal/riverine flooding (P18) –Climate change (P19)

33. Nothing –Temporal patterns (P3) –Continuous simulation (P8) –Urban drainage system hydraulics (P9) –Selection of a method (P12) –Channel losses (P17) –Risk assessment (P20)

34. Not funded –Large floods in urban areas (P14) –Storm patterns (P16) –Probability of the PMF (P24)

36. Adoption Pathways Some projects can be adopted as soon as they are available, others need to be assessed first.

37. Examples Need to assess the effect of Project 3 (temporal patterns) and Project 6 (losses) together, before adoption. They are being undertaken separately.

38. Examples Blockage guidelines (Project 11) would change current practice. Best if the whole industry moves together.

39. Some things for floodplain managers to consider Refer to new ARR methods in project briefs Ask consultants to explain how they are taking account of new methods Transition to new approaches over time Consider using old and new methods to understand differences

40. More information www.arr.org.au Water Engineering Branch Seminars