Bill Croyle stood in front of an aerial photo of Lake Oroville and swept his hand across the top of the emergency spillway that was helping drain water out of the brimming reservoir. “Solid rock. All this is rock,” Croyle, acting director of the Department of Water Resources, said with an air of confidence at the Feb. 11 briefing. The flows over the concrete lip of the unpaved spillway were tiny compared with what it was designed to handle. Oroville’s first-ever emergency spill was going smoothly.