From the New York Times:
"But California’s most troubled large dam is at Lake Isabella, built in the 1950s on what was thought to be a dormant earthquake fault by the Army Corps of Engineers on the Kern River above Bakersfield. The fault has since been shown to be active, and out of concerns that the dam could fail, the authorities restricted the level of the lake behind it. This week, officials assured nearby residents that despite heavy rains, the lake levels, and the dam itself, remained safe.
But the dam will have to be rebuilt, with a new emergency spillway, at a cost expected to be about half a billion dollars. Construction is expected to start this year and to take at least five years.
Isabella is an example of how dam spillways designed more than a half-century ago are now often inadequate, said Blake P. Tullis, a professor of civil engineering at Utah State University who has worked on the design of the new spillway. Climate change is part of the problem, he said, but other factors, like land use changes — more parking lots, for example, mean more runoff into rivers — and better weather data have also played a role.
“Now, as you do your statistical analysis, the biggest flood you could predict actually happening is much bigger,” Dr. Tullis said. “People are scrambling a bit, asking how we maintain dam safety.”"