Levee analysis: New Orleans and California
More Katrina aftershocks; Levee analysis delivers bad news for Californians
Ventura County-Star – 12/8/05
By John Krist, staff writer
When the levees protecting New Orleans failed catastrophically in the wake of Hurricane Katrina, flooding 85 percent of the city and killing about 1,000 people, the devastation also focused attention on the West Coast's own nightmare-in-waiting: the flood-prone Sacramento-San Joaquin River Delta, where a fragile network of earthen levees stands between California and disaster.
Like New Orleans, the Sacramento-San Joaquin delta is below sea level and under constant threat of inundation. New Orleans has the Mississippi River, Lake Pontchartrain and the Gulf of Mexico to contend with; California's delta is beset by San Francisco Bay and the mingled waters of the Sacramento and San Joaquin rivers, which together carry nearly half the state's runoff.
Delta levees protect the pumps driving the state's two biggest water-delivery systems, as well as critical power lines, highways, oil and gas pipelines, and deepwater shipping channels. Widespread levee failure like that in New Orleans would deal a severe blow to the California economy and threaten thousands of people.
The danger in the delta has long been recognized, at least by those in California's water and flood-protection agencies. They have called repeatedly over the past decade for the state to address the problem, but the magnitude of the task has proved to be a paralyzing hurdle.
Katrina knocked some gaping holes in that barrier. And now, three months after the hurricane transformed New Orleans into a soggy rubble heap, preliminary conclusions of the expert team assigned to investigate the levee failures there are being made public. Those findings ought to demolish any remaining political obstacles to California levee rehabilitation.
The team's final report has not been released, but the draft conclusions were reported last week by the New Orleans Times-Picayune, which interviewed the engineers and university professors hired by the state to analyze the levee failures.
The team found that only one of the New Orleans levees failed because the hurricane-driven storm surge washed over its top. Most of the flooding, the investigators found, was caused by the collapse of levees as their foundations were undermined by seepage and soil liquefaction, even though their concrete-armored tops remained well above the water level.
The reason for the foundation collapse was faulty design by the U.S. Army Corps of Engineers, according to the investigators. Steel sheet pilings that should have been driven deep into the ground to anchor the levees and prevent water from seeping through the weak soil underneath them were far too short to be effective.
The relevance of this to the situation in California's delta has little to do with the steel pilings but everything to do with the unstable nature of the ground beneath the levees and its potential to compromise an otherwise robust structure.
The ground beneath the New Orleans levees, the investigators noted, is mostly marshy soil and peat -- a very porous and weak medium. This is precisely the situation in the Sacramento-San Joaquin delta. The levees there typically rest on peat, and the embankments are largely constructed of muck dredged from former marsh.
When flood experts talk of bringing the delta levees "up to Corps of Engineers standards" -- the costly goal of most rehabilitation scenarios being discussed -- that simply means making them a little bigger and using concrete to armor their surfaces against erosion.
But as Katrina demonstrated, none of that matters when a levee's foundation is undermined. And that's precisely the greatest threat facing California: that a moderate earthquake on one of the many faults west of the delta would liquefy or deform the ground beneath the levees, causing them to collapse.
The likely consequences of such a quake were described to California water managers at a conference last week in San Diego: at least 30 levee breaks, which would flood 3,000 homes and 85,000 acres of cropland, close the Port of Stockton and two highways, disrupt electricity and natural-gas supplies, and send 300 billion gallons of sea water toward the pumps supplying drinking and irrigation water to two-thirds of California.
It would take at least 15 months and $6 billion just to repair the breaches and restore a third of the water export capacity. The total repair bill over five years would be $30 billion to $40 billion. As many as 30,000 jobs would be lost, and some parts of the delta might never be reclaimed.
The chances of such an event? About one in 300, according to Department of Water Resources Director Lester Snow.
"That was about what Katrina was," Snow said. #