If The Levees Fail In California

The good news is that Californians have heard the warnings and are starting to fix the levees. Last November they approved a $4.9 billion bond to fund repairs. But that's not nearly enough to fix the entire system, and residents now face a more vexing problem: deciding where the need is greatest.

This is a challenge that other localities face as they rush to fix aging bridges, roads, rails, and power plants in the wake of the collapse of the I-35W bridge in Minneapolis. Allocating repair money intelligently requires assessing risk accurately. That obliges policymakers to make smart predictions about weather, demographics, and countless other factors.

To guide their choices in the delta, officials are relying on a groundbreaking threat-assessment model devised by a team of 300 top scientists and engineers organized after Hurricane Katrina. It's far from perfect, but it's the most sophisticated tool of its kind ever developed and could one day become a template for guiding infrastructure investment in other areas. "We built a 200-pound bicycle," says team leader Ed (Lewis E.) Link, a senior fellow in civil and environmental engineering at the University of Maryland. "Each time it is used to measure risk in other areas, it will go faster."

Taking a spin on the 200-pound bike gives a sense of the dizzying array of factors to consider in making infrastructure investments. Developed to help organize the emergency reconstruction of New Orleans' flood defenses, the model seeks to analyze a wider range of information than had gone into earlier risk- assessment models