2011 - This is how the spillway is designed to work.
Feb 7 - residents visiting the spillway noticed water shooting upwards from the spillway whilst an ongoing flood release of 50,000 cubic feet per second was occurring.
After closing the spillway to investigate, a crator was discovered. High inflows to Lake Oroville forced dam operators to continue using the damaged spillway, causing additional damage.
Human for scale - this thing is enormous! The spillway hole had grown to 300 feet (91 m) wide, 500 feet (152 m) long and 45 feet (14 m) deep.
Feb 11 - the emergency spillway (also known as auxiliary spillway) began carrying water for the first time since the dam's construction in 1968.
Feb 11 - The flow topped out at 12,600 cu ft/s and the water flowed directly onto the earthen hillside below the emergency spillway, as per design. However, headward erosion of the emergency spillway threatened to undermine and collapse the concrete weir.
Feb 12 - an evacuation was ordered for those in low-lying areas along the Feather River Basin in Butte, Yuba and Sutter counties, due to possible failure of the emergency spillway. The flow over the main spillway was increased to 100,000 cu ft/s to try to slow erosion of the emergency spillway.
The water from the emergency spillway continued to flow heavily making its way downhill.
The amount of erosion caused the worry that the emergency spillway wall could fail and release ~30 feet of water.
Feb 13 - The damage caused by the emergency spillway overflow was made clear the next day as the dam level dropped.