Monday, January 28, 2008

Determining Flood Risk

Considering that Folsom Dam was designed as the permanent solution for flooding on the American River (using the old system) yet Folsom Lake was filled within a few weeks from an unforeseen storm, it is good a new method has been developed for use.

Why Natomas levees flunked
U.S. agency used a new type of flood-risk analysis; critics fear faulty premises could distort the results.
By Matt Weiser -
Published 12:00 am PST Monday, January 28, 2008

When the U.S. Army Corps of Engineers two weeks ago revealed that Natomas levees are not tall enough to contain even a modest storm, it wasn't because the levees had shrunk overnight or because someone misread the yardstick.

Instead, the corps applied a new yardstick.

But the new method is so complex that many flood-control experts are struggling to understand it – even some within the corps itself, said Joe Countryman, former chief of civil works design in the corps' Sacramento District and now president of MBK Engineers, a flood-control consultancy.

"It's not being demeaning to say a lot of people at the corps do not understand this," he said. "It is extremely complex."

Still, the corps intends to use its more complex yardstick to certify all new Central Valley levees. So billions of dollars and thousands of lives may be at stake.

Known as "risk analysis," the new method uses statistical modeling to estimate the range of uncertainty behind water surface calculations. The results may require not just taller levees, but ones that come with a greater assurance of safety.