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Have Oroville Dam’s Risks Become Unmanageable?

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Mining Risk Assessment

In the case of Oroville Dam, the population exposed to the potential dam failure has increased significantly. Normalization of deviance increased the probability of failure. So, is it possible that Oroville Dam’s risks became unmanageable?

Have Oroville Dam’s Risks Become Unmanageable?

When looking at risk mitigation, the old saying is that you can either lower the probability or lower the consequences. That statement requires some explanation. Indeed, what mitigation alone can do is exclusively to reduce the probability of failure. In the case below, this will not change the blue area.

In order to reduce consequences (i.e. the damages within the blue area), one has to change the system. In the case of Oroville Dam, one can reduce the probability of failure (of any part of the system) by reinforcing, mitigating, etc. However, reducing the consequences may require, for example, moving population and infrastructures away from the blue zone.

Responding to a California Public Records Act request by NSPR, state officials released a 2006 map. They revised it in June 2016 showing the extent of flooding if Oroville Dam failed with full reservoir.

The Recurring Question

Clients regularly ask us to advise if a risk is manageable or not. So, we thought we could share our thoughts and analysis process to answer this question.
The question is actually more complex and should sound like this: Which risks are:

  1. tolerable?
  2. intolerable but manageable, thus can be mitigated to reduce the probability of failure?
  3. intolerable and unmanageable and hence require strategic shifts (altering the system)?

At the inception of the dam, California provided specifications for the design of the dam in the form of the FoS which indirectly defines a likelihood of failure pf. But at that time, and even now, the FoS-pf relationship was not established.

The dam was therefore considered safe. Today, if an engineer evaluates a probability of failure and estimates consequences of a failure, he can compare the risk to a selected tolerance threshold. That threshold can be regional, national, etc.

The reply to the questions above is possible using appropriate risk analysis techniques.

The Potential Exposed Population Grew

Mitigations aiming at reducing the likelihood of failure or increasing the overall FoS are likely  financially inconceivable. They are beyond the present repair works plan, which only sets out to bring the dam back to a point in history. Even the feasibility of the repairs is uncertain, given the size of potential damages or damageable infrastructure.

In the aftermath of major catastrophes, especially nuclear ones like Chernobyl and Fukushima, people are evacuated. The evacuation can last a few years or in perpetuity. Such a move is very hard to justify as a preventative measure. Small-scale, well-documented cases of necessary evacuations have occurred around the world, and are often accompanied by legal action against the authorities/decision-makers.

So, in the case of Oroville Dam, it seems that the only other possible strategic shift could be to permanently reduce the stored volume of water.

Tools Exist

Did Oroville Dam risks become unmanageable? We have not performed an analysis, but it seems that the state of California did, and the available options are rather limited. The selection of alternatives requires an attentive comparative risk assessment, such as one provided by ORE, and beginning-to-end service/maintenance risk-informed cost analysis such as provided by CDA-ESM.