> Continued erosion of Oroville Dam’s main spillway part of ‘normal process,’ state officials say
The badly damaged main concrete spillway at Oroville Dam was pounded by massive volumes of stormwater this month, but its failures occurred well short of the maximum flow that engineers designed the system to handle.
The spillway began breaking apart when its gates were opened Feb. 7, allowing 55,000 cubic feet of water per second to roar down the slope. That was only 18% of the 300,000 cubic feet of water the channel was designed to carry per second, one of the factors that raise significant questions about its design integrity, engineering experts said. Eventually, the gash that opened up had grown to 500 feet in length and dug a hole 45 feet deep in the earth.
http://www.latimes.com/local/california/la-me-ln-oroville-spillway-damage-20170220-story.html
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The spillway was destroyed at 18% rated capacity.
Hydraulic Model Studies of the Flood Control Outlet and Spillway for Oroville Dam - California Department of Water Resources
https://www.usbr.gov/tsc/techreferences/hydraulics_lab/pubs/HYD/HYD-510.pdf