Living with levees: using tolerable risk guidelines in California

Transcription

1 Living with levees: using tolerable risk guidelines in California Jessica Ludy, CFM. Arcadis-U.S. Inc. Larry Roth, G.E., P.E., Arcadis-US, Inc. Dustin Jones, P.E., Delta Stewardship Council 1

2 Hoogwater Guus Schooneville store it convey it to the sea let it flood 2

3 When it comes to levees: two types Those that have been overtopped by floodwaters... William Hammond Hall

4 When it comes to levees: two types Those that have been overtopped by floodwaters... and those that will be overtopped by floodwaters William Hammond Hall

5 When it comes to levees: two types It should be fully understood then, that floods will occasionally come which must be allowed to spread William Hammond Hall

6 Risk cannot be eliminated California Delta Houston, Texas, May

7 Well, what level of risk is tolerable? How safe is safe enough? Understanding tolerable (and intolerable) risk helps guide the level of investment appropriate to reduce risk 7

8 Outline Risk and tolerable risk Using tolerable risk in floodplain management Case Study: California Bay-Delta 8

9 What is risk? What are the hazards and how likely are they to occur? How will the infrastructure perform in the face of these hazards? Who and what are in harms way? How susceptible to harm are they? How much harm is caused? USACE 9

10 Risk = Probability x Consequence 10

11 We make decisions every day based on what level of risk is tolerable to us 11 11

12 Yet, we (still) aim for the 1%. 12

13 The 1% flood that is 13

14 Higher design standards Red River Basin (US and Canada) 14

15 Higher design standards New York City 15

16 Higher design standards The Netherlands (sorry, I had to go there) 16

17 What guidance do we have? 1% aep National Flood Insurance Program (44 CFR 65.10) 100 year level of protection 17 17

18 What guidance do we have? 0.5% aep for California urban areas 200 year level of protection (California State Legislature, water code (n)) 18 18

19 What guidance do we have? Hazard Mitigation Plan (*MOU between FEMA and the State of California) 19 19

20 What guidance do we have? Public Law (US Army Corps of Engineers) 20 20

21 Challenges with this approach None are safety standards 1/100 yr. is a levee design standard for NFIP Insurance and development focus 1/200 yr. is levee design standard HMP is an interim disaster rehabilitation guideline PL is a disaster rehabilitation guideline Geometry based, focus on water surface elevations, say very little on performance 21 21

22 This approach focuses on the hazard Communicates that risk can be eliminated Lends itself toward structural measures 22

23 Design-based standards ignore residual risk 23

24 1% chance called into question 24

25 Teton Dam Failure Big Dig Tunnel Collapse Failures of critical infrastructure I-35W Bridge Failure Katrina Flooding 25

26 Critical Infrastructure systems must hold paramount the safety, health, and welfare of the public it serves Exercise sound leadership Use a systems approach Adapt to change Understand, manage, and communicate risk 26 26

27 How do you manage risk? American Society of Civil Engineers

28 Leaders use risk informed analyses Tolerable Risk How to apply it Risk-informed mapping 28 F-N curves 28

29 Eliminating risk is impossible Tolerable Risk is the level of risk that people are willing to live with in order to secure certain benefits. Unacceptable Tolerable Broadly acceptable Range of Tolerability Risk cannot be justified except under extraordinary circumstances No further actions required. Risk regarded as insignificant 29 29

30 Tolerable risk United Kingdom 30 30

31 Tolerable risk principles (HSE 2001) Life safety is paramount Risk cannot be ignored Absolute safety cannot be guaranteed Equity Efficiency Individual risk Societal risks Goal = Reduce risk to as low as reasonably practicable (ALARP) 31 31

32 Using tolerable risk guidelines enables Full consideration and communication of hazard and consequence Consistent and transparent approach to reducing risk Enables systems approach Allocate scarce resources and focus on most urgent risks first Evaluates tradeoffs 32

33 How do you use tolerable risk to make decisions? Assess, characterize, and evaluate risks Unacceptable Tolerable Broadly acceptable Risk cannot be justified except under extraordinary circumstances No further actions required. Risk regarded as insignificant 33

34 Frequency of (n) or More Fatalities per Year 10-1 PROBABLY NOT GOOD GUIDANCE DEFINED BY USACE AND USBR PROBABLY OK ,000 10,000 Number of Fatalities (n) F-N CURVES 34 34

35 Frequency of (n) or More Fatalities per Year MERCHANT SHIPPING PROBABLY NOT GOOD KATRINA FOUNDATIONS FARM ACCIDENTS 10-5 DAMS PROBABLY OK COMMERCIAL AVIATION ,000 10,000 Number of Fatalities (n) F-N Plot

36 Frequency of (n) or More Fatalities per Year Reduce risk to tolerable levels UNACCEPTABLE RISK Non-structural solutions e.g., improved evacuation Structural solutions e.g., stronger levees TOLERABLE RISK Goal = ALARP, as low as reasonably practicable ,000 10,000 Number of Fatalities (n) 36 36

37 Life safety risk posed by levees Netherlands tolerable risk guideline 37

38 Applying tolerable risk guidelines in the California Bay Delta The Delta 38

39 Sacramento Suisun Marsh Sacramento San Joaquin Delta San Francisco Bay Stockton Pacific Ocean 39

40 California Bay Delta and Suisun Marsh 1,100 miles levees Roughly 60 islands Water Supply 25 million 4 million acres Ecosystem Agriculture 500,000 people 40 Delta Plan, 2013

41 Delta land elevation and subsidence Public Policy Institute of California 41

42 Delta levees Wet/dry Project/non-project 42

43 Delta levees Levees built for one purpose now serve another 43

44 Delta flood risks-hazards Flood (high water) Earthquake Condition of levees Subsidence Seepage Jones Tract, Sunny day failure

45 Delta flood risks-consequence 45 45

46 Delta Reform Act: levee investment strategy to reduce risks Life & property State Interests Coequal goals: Ecosystem Water Supply Delta as a Place 46 46

47 Step 1: Assess flood risk in the Delta (today and in the future) 47

48 Step 2: Map flood risk in the Delta AGGREGATE RISK AGRICULTURE RISK ECOSYSTEM RISK WATER SUPPLY RISK FLOOD DAMAGE RISK (EAD) LIFE LOSS RISK 48 48

49 Frequency of (n) or More Fatalities per Year Set tolerable limit lines 10-1 PROBABLY NOT GOOD Line must be set by policy and informed by analysis PROBABLY OK ,000 10,000 Number of Fatalities (n) 49 49

50 Step 3: Act

51 Characterize risk Immediate attention? 51 51

52 Identify options to reduce risk Non-structural measures c Structural measures c 52 52

53 Characterize risk Are there additional areas that could be considered for more urgent attention? 53 53

54 Identify options to reduce risk Non-structural measures c Structural measures c 54 54

55 Do measures reduce risks to tolerable levels? What are the tradeoffs? 55

56 Effects of improved evacuation and levee conditions on risk 56

57 Iterative approach CHARACTERIZE RISK -START WITH RISKIEST ASSESS RISK (CONTINUOUSLY REVIEW) IDENTIFY PROJECTS TO REDUCE RISK TO TOLERABLE LEVELS ASSESS,CHARACTERIZE RESIDUAL RISK -ELEVATE RELATIVE URGENCY BASED ON ASSETS 57 USE EXPERT JUDGMENT

58 Next steps for us Identify and evaluate measures to reduce risk to tolerable levels Evaluate tradeoffs Develop a comprehensive investment strategy in the Delta 58

59 Why tolerable risk? We know the problems with design-based standards Life safety paramount Recognizes that absolute protection is not possible Communicates risk clearly Manages risk with all available options 59 59

60 Why tolerable risk? Guides decision making Allocates finite resources over 1,100 miles of levees Identify which levees pose the greatest risk Suggests which actions to take first Level of risk in relation to tolerable risk 60

61 Why tolerable risk? Because floodplain LEADERS will use risk to make decisions in floodplain management 61

62 Thank you. Our partners: Delta Stewardship Council Rand Corporation Environmental Science Associates Shannon and Wilson Catalyst California Contact: 62