Comments on: On High-Probability, High-Consequence Events

By: 10 Interesting Links From April 4th | Greg In The Desert

10 Interesting Links From April 4th | Greg In The Desert — Sun, 05 Apr 2009 07:03:39 +0000

[...] jfleck at inkstain » On High-Probability, High-Consequence Events – My friends in the nuclear weapons community have, over the years, helped me understand the tools for thinking about low-probability, high-consequence events, like a warhead accidentally going off. You really don’t want that to happen, so even though averaged across all possible futures the average badness might be relatively low, it’s worth spending some time and energy thinking through ways of reducing the probability of the high-consequence event. [...]

By: Eric Fairfield

Eric Fairfield — Mon, 30 Mar 2009 23:18:35 +0000

It appears that the calculated probability of failure in the PPIC report (which I have not read in its entirety yet) is (1 – probability of not failing) and the probability of not failing is viewed as a constant for every year from now until 2050.

If the yearly probability of failing is 7% then the yearly probability of not failing, for this example, would be 93%.
Does anyone know whether this constant yearly probability of failing is a reasonable assumption for the Sacramento delta?

I would think that the probability of failing each year is not a constant but depends on what happened last year. For instance, if there was a small earthquake one year, one that would not generate a real failure, then the levees would be strengthened and the probability of failure in the following year and for subsequent years would drop dramatically.

In statistical terms, such a process is not modeled by a constant probability of failure but is often modeled by a Monte Carlo version of a Markov process. In such a modeling, small partial failures are included and modify subsequent yearly predictions. The Monte Carlo approach comes in because it is not known in what year the small failure would occur so averaging over each possible occurrence is important.

Could someone tell me where the failure estimate in this report came from and whether the assumptions about failure are generic or are matched to real world events, such as partial failures, changing technology, or changing political climate?

Thanks,

By: Steve Bloom

Steve Bloom — Sun, 29 Mar 2009 21:19:11 +0000

The report basically recommends accepting that most of the islands will have to be abandoned (flooded) and that a PC is the only practical option for maintaining exports in the face of this change. That degree of realism is a step forward, but the problem is that unlike the present water transfer arrangement a PC will make possible the near-complete destruction of the Delta ecosystem. I’m not sure it’s going to be possible to pass any sort of PC proposal without requiring massive changes in Central Valley and SoCal water use, but I’m pretty sure they’ll try to pass a window-dressing-only version before considering any such thing. Note that the principal funder of the study was Stevie Bechtel, it being a small world after all.

I’ll look forward to your post, David.

By: David Zetland

David Zetland — Sun, 29 Mar 2009 17:26:53 +0000

I will blog on this (thanks for reminding me), but I will note right now that failure of the levees (really dikes, since the “islands” are really polders, i.e., below sealevel…) would mean little to the ecosystem, a LOT to the people with land underwater and MUCH MORE to the delta water exporters…

That’s their excuse for a peripheral canal, but it’s my excuse to see that SoCal lives off “its” water. I am NOT saying this as a NorCal partisan, but as someone tired of the bad economics/ecology of moving water all over the place.