April 9, 2007
The Auburn Dam has officially been resurrected from the dead. The last post I wrote warned that proponents of the dam were gaining momentum in D.C |well now they’re off and running.
David Whitney, of the Sacramento Bee, reported on Friday that a House hearing Thursday on protecting the Sacramento-San Joaquin Delta from catastrophic levee failures turned into a mini-rally for constructing an Auburn dam on the American River.
Congressman Doolittle is using 1965 authorization for the dam as justification to go ahead with securing funding for its construction, and his influential congressional allies in the House Appropriations Committee are using every opportunity they can to promote and push the project during House deliberations.
Their main arguments in favor of the dam? That it is the only way to achieve 500 year protection for the Sacramento area, and that it would relieve pressure on downstream levees.
Heres the problem: Regardless of how many dams there are upstream releasing water into the levees during a flood, they still need to be able to handle the large amounts of controlled releases that could currently destoy them. Also, even if Auburn is upstream letting out water gradually into Folsom, Folsom will need to be able to let water out faster than its current capacity for doing so if Auburn is to have any helpful affect whatsoever.
Bottom line? Levee repairs and Folsom Modifications are needed first¦NO MATTER WHAT. So why spend money on more studies and deliberations, when there is a solid, clear need that keeps getting ignored? Lets fix the immediate, obvious problem first. THEN we can decide what added protection is desired.
As for that later debate, and 500 year protection, there are several different ways at analyzing and projecting flood risks. The 500 year number refers to a modeled probability based upon statistical extrapolation. Translation? The flow level associated with a 500 year event is a flow level that has never been seen in recorded history, but that in a mathematical model has a projected 1 in 500 chance of occuring in any given year.
The most important thing to know about this modeled probability is that the Army Corps of Engineers themselves, (the government agency responsible for creating the statistical model), admitted in their report that the model was NOT MEANT TO EXTRAPOLATE, WITH ANY ACCURACY, FLOW FREQUENCIES BEYOND THOSE WITH A 1 in 200 CHANCE OF OCCURING. Why? Because the mathematics break down beyond an interval that is more than twice the length of the available data set. And the available data set happens to only be 100 years long.
So, perhaps the Corps frequency model isn’t the best way to try and predict the maximum flood that can be reasonbly expected from the American River Watershed. (They even say so themselves!)
An alternative is to use what is referred to as the Galloway method, in which public projects are built based upon what is called the â€œstandard project flood.â€ Had this analytical method been applied in New Orleans, their system of flood protection wouldn’t have come near the standard project flood requirements, and they may have then had the chance to avert disaster. Why? Because in determing the standard project flood, analysts take the local weather system and data into account, placing the worst possible storm directly above the watershed and determining what the resultant runoff would look like. New Orleanâ€™s levee and dam system was not built to withstand a Class 4 or 5 Hurricane, even though those storms appear in the Gulf every few years! In contrast, Northern California only has one, very consistent storm to worry about: the “Pineapple Express.” [Read more about this in post titled, Katrina Disaster Unfortunately Drawing Ill-Founded Support for the Auburn Dam.]
So what’s the point of all these ramblings? Well, Auburn Dam would have several negative affects on top of drowning two incredibly valuable and beautiful river canyons. One, it would cost an incredibly large amount of money to build. Two, geologists at the USGS believe there is a lot of unresolved uncertainty surrounding the very dangerous possibility that the damâ€™s location along a fault system could trigger a devastating earthquake. Three, its water would be too limited and expensive to have hopes of paying off the dam any time in the near future.
With environmental and economic losses so big, is it really worth building a structure based upon a projected risk that is an unreliable estimate at best? Perhaps we should look instead to the numbers that can be trusted:
Sacramento is NOT currently protected against a 200 year event, and CAN BE with repairs to levees and Folsom Dam. Should there even be a debate as to what to do next???