This story from Sunday’s bee reminds us, yet once again, how bad decisions by public leadership can result in such tragic events as happened in New Orleans, and continues to threaten the Sacramento area.
The story of the Natomas levees is the story of our region and promotes the same conclusion, we need to get it right and we can get it right. Lives really do depend on us getting it right.
Here is an excerpt.
Tempting fate: Bad assumptions undermine levees
By Carrie Peyton Dahlberg -- Bee Staff Writer Published 2:15 am PDT Sunday, April 9, 2006
On a cloudy February day in 1998, the Army Corps of Engineers wrote Sacramento flood officials to tell them that Natomas, a deep floodplain with wide stretches of undeveloped land, had been fortified against 100-year floods.
It was what everyone had been waiting for. It would lead to cheaper flood insurance, an end to mandatory insurance and the complete lifting of a building moratorium. It would encourage acres of new homes to spread through Natomas, nearly tripling the area's population to 67,000.
Yet that assurance of 100-year protection from rivers and canals was based on illusion.
It was founded on a series of levee studies much scantier than those recommended in the Army Corps of Engineers manual at the time or those conducted by corps districts in several other parts of the United States.
In retrospect, it's clear the corps missed basic features of the ground beneath Natomas levees because of those limited explorations, said David Ricketts, a former corps section chief who reviewed old and new Natomas findings at The Bee's request.
The misstep was fairly simple, resting in how many holes engineers drilled into the levees to bring up fat cylinders of soil. More holes give engineers more information to do lab analyses that are part art and part science, predicting how safe a levee will be if a river runs high. Will its sides slip? Will water seep through or beneath harmlessly, or will the seepage dangerously drag soil along with it?
In the late 1980s, when Natomas levee repairs were being designed, corps contractors had drilled only one hole every 2,000 feet - 2.6 holes per mile - to help answer those questions. That was two to 10 times less than recommended in the Army Corps 1978 manual, which did allow discretion because local conditions can vary so widely.
Using that discretion turned out to be a poor choice.
New studies have concluded the area would not be safe in a 100-year flood, the kind spawned by storms with a 1 percent chance of sweeping through in any year. It will cost $140 million to $200 million and take until roughly 2011 to provide that protection, according to the top engineer of the Sacramento Area Flood Control Agency.
So many factors go into assessing a levee that it would be too simplistic to blame scanty explorations alone for the different conclusions of 1998 and 2006, said Ricketts and many other geotechnical experts. Corps engineers stress that a later flood helped them learn from their mistakes.
And yet, two things emerge plainly in the wake of the Natomas about-face:
* Today, after institutional soul-searching, the Sacramento corps' engineers and contractors are strongly encouraged to do at least 15 probes for each levee mile, and sometimes 50 or more, leading the district to warn that numerous Central Valley levees may not be up to snuff.
* Just as the definition of safety has changed sharply twice in Natomas, it could change again, as corps standards are re-examined in the wake of New Orleans levee failures, bigger storms and other developments. So even if Natomas regains 100-year protection, there is no guarantee it will keep it. And there's no guarantee for other communities, either.
"No matter what kind of levee you're behind, you should assume there's a risk," said John Hess, chief of the geotechnical and environmental engineering branch at the Sacramento corps. Each improvement lessens the risk, Hess said, and today Natomas' levees are unquestionably sturdier than before their last round of repairs.
But the risk never disappears.
