In February 2017, damage to a spillway at the nation's tallest dam placed thousands in the Butte County community of Oroville under evacuation due to the threat of flooding. The crisis began after heavy downpours drenched Northern California -- just the start of what was to be one of the wettest winters on record.
On Feb. 7, engineers noticed concrete erosion on a flood control spillway at the dam, a key component in the state's water system built in the Sierra Nevada Mountain foothills about 75 miles north of Sacramento in the 1960s. On Feb. 11, rising water levels beyond the 770-foot tall dam required use of the emergency spillway for the first time in the dam's history. Erosion at its base led authorities to issue mandatory evacuation orders on Feb. 12 due to the possibility of flooding.
That threat eased as crews shored up the spillway, lake levels dropped and the clock ticked down on California's rain season.
But the work was just beginning for construction crews, biologists, engineers, transmission line workers and others in Oroville, where work continued around the clock. The work included debris removal, transmission line inspections, wildlife relocation and months of heavy lifting to shore up and repair the spillway. By mid-March, nearly 1 million cubic yards of material had been removed from a debris pile at the base of the spillway.
The goal is to return both the gated flood control and emergency spillway back to their original design capacity. Officials said the repairs allow the spillway to operate during California's rain season.
Below, these dramatic images show how work is progressing months after the spillway crisis.