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Hurricanes in California?- Katrina Disaster Unfortunately Drawing Ill-Founded Support for the Auburn Dam

February 2nd, 2006 Robyn Suddeth

Senator Doolittle has lately been making attempts to put the Auburn Dam back on the table in national legislation. (The Auburn Dam would drown most of the Middle Fork American River canyon and half of the North Fork American.) Lending impetus to this idea is recent “That Could Happen To Us!” speculation that has followed the Hurricane Katrina disaster.

Although certainly not of the teenage-esque mindset that we are immune to natural catastrophe, I can’t help but notice elements of ignored common sense and hysteria within these recent warnings that Sacramento is doomed for the same fate as New Orleans.

To start with, Sacramento already has 100 year flood protection, and in 150 years of solid historical data has never encountered a flood larger than an 80 year event. Even so, improvements to Folsom Dam and American River levees have already been budgeted for in Governor Schwarzenegger’s Strategic Growth Plan and will bring our system up to as high as 275 year protection.

One must be weary, however, of quoting numbers such as “100 year protection” versus New Orlean’s supposed “250 year protection.”

Many people exhibit a dangerous misunderstanding of these terms: 100 year flood protection DOES NOT mean that we are protected against a flood that historically comes once every 100 years. Rather, it means that we are protected against a flood that has a projected one in a hundred CHANCE of ocurring each year. The same formula applies to “250 year protection” and “500 year protection.” Even these numbers, however, are the end points of a line that was extrapolated from real data, meaning that there is actually no historically-recorded flood as large as a 500 year event. (Or even one as large as a 100 year event for that matter.)
So what is the difference between Sacramento and New Orleans, and why am I not as worried? Well, these statistical probabilities that we base many of our flood control infrastructure upon are calculated primarily by taking historical flow measurements from a river’s watershed.

Anyone notice an important number possibly missing from this equation? I do: regional weather data may is not taken into account. And what is the first step in a river flooding? A storm.

OK, so if New Orleans was basing their level of protection upon data taken from the Mississippi River and not taking into account the likelihood that a type four or five storm would eventually hit them (Hurricane Katrina), I am led to believe that their numbers may have been a bit off.

And here is the key to why I’m not quite as worried about Northern California as many people currently are. What big storms have the potential to cause flooding here? The answer is there is only one such storm: the Hawaiian Tropic that we so recently experienced. Unlike the hurricanes the rack the Gulf every few years, it is an extremely consistent and predictable storm that we have years and years of historical data on, and it is the ONLY storm that could possibly hit California and cause the floods that we worry about.

So basically, there are no hurricanes in California.

To summarize: I believe that New Orleans “250 Year Protection” number was possibly misguided, and that our “100 Year Protection” (which is actually more like 150) is better supported. And even this number is just a probability.

With improvements to levees and the Folsom Dam, we could raise that protection to somewhere around 300 Year Protection. And in 150 years of solid data on that friendly Hawaiian storm, it has never dumped enough rain to cause a flood as large as a 300 year event. (Remember, it’s all extrapolation.)

So yes, we should definitely make flood protection a priority and push for improvements on our current system. I just hope legislation is written in a spirit of educated decision-making rather than frenzied spending; and that unecessary and environmentally harmful projects such as the Auburn dam are forever-more avoided.

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