Risk criteria with respect to asset versus system scenarios

–Focus on an island in the western California Delta, say Sherman Island, and consider criteria that engineers rely on for establishing priorities with respect to reducing levee fragility there (the island’s surrounding levees are needed because its productive areas are considerably below water level):

  • Criterion 1. Levee fragility priority can be set in terms of the weakest stretch of levee around the island, i.e., the stretch of levee that has the highest probability of failure (Pf). This has obvious implications for collocated elements from different infrastructures, e.g., a very high levee Pf should counsel against plans to place, say, a huge chemical tank facility next to it. (You’d assume commonsense would commend this as well.)
  • Criterion 2. Levee fragility priority can be set in terms of the stretch with the highest loss of life (and/or other assets) arising from levee failure. If the levee breaches where most island residents live, then there is considerably less time for evacuation. Clearly, consequences of failure (Cf) are important here, and this criterion is about the levee stretch that has the greatest risk of failure, not just probability of failure.

Sherman Island’s weakest levee stretch, at the time of research, was said to be on the southwest part of the island; the stretch with the greatest loss of life appeared to be on the eastern and south-east side (where most residences seem to be). Other factors constant and from the perspective of Criterion 2, it is better the weakest stretch of levee is on the other side of the island (according to Criterion 1), so as to ensure more time for evacuation.

–A third criterion reflects the extent to which the island’s levee infrastructure is part and parcel of a wider interconnected critical infrastructure system (ICIS):

  •  Criterion 3. Levee fragility priority can be in terms of stretch that has the greatest risk to the entailed ICIS. ICIS risk of failure is not the same as risk of levee failure only, as stretches of Sherman Island levees are in fact not just elements in the levee system there but also elements in other critical infrastructures. For example, on Sherman Island, there is the levee stretch with Hwy 160 on top; there are also other stretches that serve as the waterside banks of the deepwater shipping channels; there is another stretch that serves to protect a large wetland berm (as fishing and bird habitat). If those stretches of levee fail, so too by definition do elements fail in the deepwater shipping channel, Hwy 160 or the Delta’s endangered habitat.

Criterion 3 compels the risk analyst to ask: What is the effect on the road system or shipping system or wetlands system, when that shared ICIS element on Sherman Island fails? For instance, if a stretch of Hwy 160 fails, road traffic in the Delta would have been detoured; if a stretch of the deepwater shipping channel fails, shipping traffic would have been rerouted to other ports; and so on. Note that in some cases the service cannot continue because there are no default options, e.g., the Sherman Island wetlands berm in terms of its habitat and fish can’t be “rerouted” were its protective levee to fail.

From the perspective of Criterion 3, the risk analyst’s question with respect to the greatest ICIS risk becomes: What infrastructure system that shares one or more ICIS elements on Sherman Island would be affected the most in terms of increasing the probability of its failing as a system, were those Sherman Island elements to fail? The answer: A levee breach anywhere on Sherman Island would increase the probability of the closing the key pumps for the State Water Project. That is, the Pf of the state and federal water projects would increase were Sherman Island to flood, because saltwater would be pulled further up from the San Francisco Bay into the freshwater Delta.

–In short, the three risk assessment criteria—others are possible—differ appreciably as to where risk analysts focus attention in terms of levee fragility: the weakest stretch (Pf) may not be the same stretch whose failure would have the greatest loss of life and property (Cf), while any stretch that failed would pose the greatest ICIS risk (namely, the probability that an ICIS element failing increases the failure of one or more of the constituent systems sharing that element). In the latter case, the risk not only for the adjacent levee system in the western California Delta (i.e., a failure of Sherman Island levees would increase erosion and seepage pressure on islands next to it), but also for the freshwater supply system from the north to the south of the State.

You would expect that calls for more and more “inter-organizational coordination” would have to be prioritized in light of these distinctions. You’d be wrong, worse yet for infrastructures whose technical cores are already so complex as to require the full time attention of their respective reliability professionals.

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