Flow (Flood) Numbers and Estimates

The Numbers:

• 500 year event: a 1/500, or 0.002 probability that the American River produce flows of ~520,000 cfs, which is 80% greater than any historically-recorded flow.
• 250 year event: a 1/250, or 0.004 probability that the American River produce flows of ~400,000 cfs, which is 50% greater than any historically-recorded flow.

How The Numbers Were Calculated:

• Corps of Engineers, NRC, and The Bureau of Reclamation all put forth different frequency estimates.
• Corps of Engineers used mathematical computer model… took 100 years of stream flow data and plugged it into the model. Model then generated frequency estimates both for those flows and flows never before recorded.
• Parameters Assigned: NONE!

The Variables That Affect Real Flows:

• Precipitation, current water levels, current snowpack
• Size and existence of Pineapple Express storm
• Global Warming
• Reason to believe these (storm size and global warming effects) should or shouldn’t have a limit on them???

Earthquake Numbers and Estimates

The Numbers:

• 2 to 30% chance that filling a reservoir at Auburn would trigger a large quake. This translates to a 0.02-0.30 probability, or a 1/50 chance.
• Need to know the percent chance that this resultant quake is then >6.5, or big enough to create displacement > the Bureau’s estimated 5 inches. (The new gravity dam is based on these numbers.)
• Finally, what is the percent chance, then, of dam failure?
• It may still be bigger than 1/500!!
• USGS warns of a greater degree of uncertainty than the Bureau is basing its estimates upon.

The Variables That Effect Quake Size and Occurrence:

• Water Weight (related to depth of reservoir)
• Fault Activity- Oroville suggests the faults are active
• Draw-down and refilling of reservoirs has been linked to reservoir-induced seismicity.

*THE POINT: AN EARTHQUAKE AS A RESULT OF AUBURN IS MUCH MORE “LIKELY” THAN THE FLOODS THE DAM IS SUPPOSED TO PROTECT US FROM!