Oroville Dam crisis

In early February 2017, Oroville Dam's main and emergency spillways both sustained damage during a period of sustained outflow from Lake Oroville, leading to the evacuation of areas downstream. Severe rainstorms and snowstorms impacted California, which, after being in a state of drought for five years, was not environmentally capable of absorbing the excess precipitation into the ground. The lake levels began rising rapidly following another wet storm in early February, and soon began flowing out of the main spillway. Damage to the spillway was first noted on February 7; as the spillway continued to degrade, the decision was made to reduce its outflow by utilizing the emergency spillway on February 11, 2017, which had not been used since the dam’s construction, which consisted of a barren hillside. The hillside began eroding much faster than had been anticipated, particularly at its top, and this headward erosion threatened to undermine the concrete weir at the top of the emergency spillway, which could have sent a 30-foot (10 m) wall of water into the Feather River below and flooded communities downstream. On February 13, as authorities oversaw the evacuation of more than 180,000 people living in the threatened areas, mainly those in Butte County, Yuba County, and Sutter County, emergency reinforcements were added to the emergency spillway and the outflow through the main spillway was increased again, which significantly exacerbated the damage to the main spillway and the adjacent hillside. On February 14, amidst declining outflows and the cessation of flow through the emergency spillway, the evacuees were allowed to return. Repairs to the dam were substantially complete by 2019.