I think that it means that the gate breaks free, or partially free of its mooring and is thus either stuck in a cockeyed position or blown down the spillway. Meaning that 1 of 8 gates will no longer have a door. Water will spill through that one until the reservoir level drops below about 812 feet +/-.
10 day lake forecast inflow, outflow, elevation
https://twitter.com/KCRAMax/status/852625562229129216/photo/1