Risk and Safety in Engineering: Lessons from Hurricane Katrina. Byron Newberry Mechanical Engineering

Transcription

1 Risk and Safety in Engineering: Lessons from Hurricane Katrina Byron Newberry Mechanical Engineering

2 Is Katrina an engineering ethics issue? There was no evidence of government or contractor negligence or malfeasance the system was generally built as designed, and design approaches were consistent with local practice. IPET* Draft Final Report 1 June 2006 *Interagency Performance Evaluation Taskforce

3 Beyond the basics Not being negligent, not being malfeasant, building to design, and designing according to established practice are all basic requirements for good, ethical engineering practice, but they do not always eliminate the possibility of failure, particularly for complex systems things can go wrong even when everyone is trying to do the right things, and trying to do them well

4 Costs of Failure This event resulted in the single most costly catastrophic failure of an engineered system in history. NSF Report, July 31, 2006 ~$200 Billion in damage ~1500 dead ~450,000 displaced, 200,000 permanently

5 Advanced ethical responsibility Conscientiously striving to understand and avoid the subtle and insidious pitfalls both technological and organizational of complex systems is an ethical responsibility

6 So what are some of the pitfalls that can be identified from Katrina? Unanticipated failure modes Faulty communications: feeding back and using new information Faulty assumptions Incomplete knowledge Lack of conservatism & redundancy Changing conditions over time Risk psychology Physical interfaces and transitions Organizational interfaces and transitions Competing interests Organizational inertia Historical contingency & lock-in

7 Unanticipated failure modes

8 Unanticipated failure modes The following failure mode was not considered in the design of the canal levees, but occurred at locations along the 17 th Street and London Ave Canals Hydrostatic Pressure Gap Shear area Reduction of shear area by half

9 17 th Street Canal Failure

10 Gap on east bank of IHNC

11 Faulty Communications: feeding back and using new information Experimental tests were performed in the 1980s by the USACE on full-scale levee/sheetpile/floodwall systems. Results of the tests demonstrated the potential for a failure mode resulting from a gap developing at the outboard face of the sheet pile This information appears never to have been adequately transmitted to engineers in the field nor to have influenced design practice

12 Faulty Communications: feeding back and using new information The New Orleans Hurricane Protection System was originally designed to protect against a Standard Project Hurricane (SPH), the specifications for which were developed in the 1950s. Over the years, the SPH became the unquestioned standard for the worst case scenario, even as the details and limitations of its origin were lost from view. Enormous advances in atmospheric sciences post- 1950s were never used to adjust or improve the design specifications

13 Faulty assumptions Using average values of soil strength based on widely spaced borings over a highly variable area Assuming the soil shear strength under the levee center is a representative value, rather than the maximum that it is The SPH (standard project hurricane) the design was based upon was thought to be a once in year scenario Basing elevations off of an incorrect datum

14 Faulty assumptions: Datum Flood control structures in the region were authorized and designed relative to a water level datum (mean sea level), but constructed relative to a geodetic vertical datum incorrectly assumed to be equivalent to the water level datum. This resulted, in the case of the outfall canals, in structures built approximately 1 to 2 ft below the intended elevation. Updating of the reference elevation points for the region, although underway, was not completed and left decision makers without an accurate understanding of the actual elevations of the hurricane protection.

15 Incomplete knowledge The science of analyzing storms and predicting their behavior has improved dramatically since the design and construction of the New Orleans hurricane protection system (HPS) was first initiated. The understanding of interrelationships of river systems, wetlands, barrier islands, flooding, and storms has improved dramatically Improved engineering design/analysis tools techniques (soil testing, structures, hydrology, etc.)

16 Lack of redundancy Series system One part fails, the system fails The central concept of [the Dutch] strategy is the controlled flooding of compartments of limited size, thus limiting the affected area and minimising the flood damage. It means designating areas for temporary water storage and dividing the existing large continuous dike-rings (areas surrounded by a dike) into smaller compartments with different flood probabilities. Vis, Klijn, de Bruijn, van Buuren, Int. J. River Basin Management, 2003

17 Lack of conservatism Low margins of safety used despite magnitude of risk Typical levee factor of safety: 1.3 Design practice historically evolving out of levee construction in rural areas, agricultural land not intended for, and never modified for, protection of large populations/high value developments Not in line with factors of safety required for dam construction

18 Lack of priority Plaquemines Parish Pop: ~27,000

19 Changing conditions over time Physical Land subsidence Coastal erosion Societal Continual development of low lying areas Increase in population and property improvements Changing political and economic factors affecting project Flood control isn t just a series of construction projects; rather it has to be a continuous process of adapting to changing conditions

20 Risk psychology After the fact of Hurricane Katrina The group faulted the agency responsible for the levees, the Army Corps of Engineers, for adopting safety standards that were "too close to the margin" to protect human life. Well before Hurricane Katrina Orleans Levee District officials believed that the Corps standards may be too high They recommended the Corps lower its design standards This, they believe would make the project more affordable, provide adequate protection, and speed project completion 1982 GAO report In several instances, State agencies pressured for 'lower cost' solutions not realizing that these solutions would result in lowering the overall quality and reliability The more one invests in mitigation, the less one is likely to continue to invest because of a decrease in negative feedback.

21 Physical interfaces and transitions Physical transitions between types of barriers (e.g., levee with I-wall transitionin g to bare levee)

22 Physical interfaces and transitions Interfaces between barriers and other infrastructure (railways and roadways)

23 Organizational interfaces and transitions USACE design and construction of levees Local Levee Districts operation and maintenance of the levees New Orleans Water and Sewerage pumping stations and outflow canals Various other entities (railroad companies, DOT, etc) at specific locations/penetrations

24 Competing interests The original design the barrier plan called for barriers at the inlets to Lake Pontchartrain to prevent storm surges from entering lake. The corps proposed butterfly valves at the outlets of the drainage canals at Lake Pontchartrain, to prevent storm surges entering city. This plan was abandoned after years of litigation. The Water and Sewerage Board defeated the plan politically because of questionable concerns about the impact on their operations

25 Competing interests The USACE had tried for many years to obtain authorization to install floodgates at the north ends of the three drainage canals Dysfunctional interaction between the local Levee Board (who were responsible for levees and floodwalls, etc.) and the local Water and Sewerage Board (who were responsible for pumping water from the city via the drainage canals) prevented the installation of these gates, however, and as a result many miles of the sides of these three canals had instead to be lined with levees and floodwalls.

26 Organizational inertia & bureaucracy complacency & funding Various articles presciently predicted the results of Katrina years in advance. The Corps knew of subsidence problems, improved storm forecasting, etc., for years Comprehensive plans to mitigate problems with the entire coastal Louisiana region were developed (e.g., Coast 2050)

27 Organizational inertia & bureaucracy complacency & funding The northeast flank of the St. Bernard/Ninth Ward basin s protecting ring of levees and floodwalls was incomplete at the time of Katrina s arrival. The critical 11 mile long levee section fronting Lake Borgne was being constructed in stages, and funding appropriation for the final stage had long been requested by the U.S. Army Corps of Engineers (USACE), but this did not arrive before Katrina struck For many years, the Corps of Engineers has been subjected to extreme pressures at the federal and state levels to do more with less; to do their projects better, faster, and cheaper

28 Organizational inertia & bureaucracy complacency & funding intrinsic risk associated with over-long project durations for these types of massive, regional scale projects. Also that both White House and Congressional attention lapsed, and funds that could have been provided to complete these important levees were instead deferred, as issues elsewhere drew more urgent attention.

29 Organizational inertia & bureaucracy complacency & funding Splash protection on backside of floodwalls low cost fail-safe measure in case of overtopping ( estimated at less than 5% of the overall project section cost ) The USACE were instructed by Congressional edict to design for a specified water level, and to install splash pads would be to provide for a higher level than that which had been authorized.

30 Historical contingency & lock-in Levee system developed piecemeal over 200 years new solutions tend to be extensions of old ones. Storm protection is a locked-in problem for New Orleans. River control is a locked-in problem for New Orleans.

31 Historical contingency & lock-in Old River Control Structure