PDF version online of full USGS Arkstorm report

• Report PDF (9.8 MB)
• Appendix A PDF (2 MB)
• Appendix B PDF (598 kB)

• This report is available only on the Web.

One of the scarier things they talk about in this report is the potential for raw sewage running down the Los Angeles River to the Ocean which might create evacuation situations in various localities. Because you have at least 14 million people in the greater Los Angeles County area which likely includes Orange county at least too this makes sense if flooding overwhelmed sewage treatment plants in various areas.

I think sewage treatment plants would be built at the lowest possible elevations to protect the local populations from events just like this. But, if flooding hit those lower areas then raw sewage would be everywhere below a certain elevation throughout the Los Angeles area based upon the quickest way to the ocean over land from that location in relation to gravity and slope. So, there likely would be no way to protect against an Arkstorm in what it would do if flooding was beyond a certain point.

So, if you imagined the Los Angeles Cement rivers overflowing into nearby cities full of sewage this is one of the problems likely one would encounter in events like the 1861-62 floods if and when they happen again. And since historically there have been 6 events in the last 1800 years in the western states worse than the 1861-62 floods it might be inevitable. The only question is "When?"

But, unlike earthquakes predicting when such events might occur is much easier than predicting earthquakes. So, we might have a few days notice from meteorologists when such events take place in the future so we know when to evacuate large areas in preparation for such an event.