from LA Times:
The damage occurred even though the spillway was designed to handle much more water than the amount that overflowed. Some questioned why officials didn’t heed suggestions more than a decade ago to fortify the emergency spillway.
Earth and weak rock near the top of the spillway started to erode when peak flows were 12,600 cubic feet per second, compared with the designed capacity of 450,000 cubic feet per second, according to the Department of Water Resources. The erosion happened so quickly that officials feared the concrete wall would be undermined, and ordered sweeping evacuations in Butte, Yuba and Sutter counties that remained in effect.
With more storms expected to slam Northern California later this week, officials worked frantically Monday to drain water from brimming Lake Oroville in hopes of heading off a potentially catastrophic flood.
ill Croyle, the acting director of the Department of Water Resources, said Monday that he was “not sure anything went wrong. This was a new, never-happened-before event.”
But during 2005 relicensing proceedings for Oroville Dam, several environmental groups argued that substantial erosion would occur on the hillside in the event of a significant emergency spill. In a filing, they asked the Federal Energy Regulatory Commission to order the state to “to armor or otherwise reconstruct the ungated spillway.”
State Water Project contractors, including the Metropolitan Water District of Southern California, were involved in the relicensing. MWD General Manager Jeffrey Kightlinger said Monday his agency deferred to the state and federal agencies on the matter.
“They did look at that issue and they determined that [the existing emergency spillway] did meet the appropriate FERC guidelines,” Kightlinger said. “In the FERC guidelines, they talk about how you don’t put a lot of funding and concrete, etc. into emergency spillways because presumably they will rarely if ever be used.”
“We did not say it was a cost issue,” he added.