Construction of a new spillway at the Oroville Dam in northern California—the largest dam in the U.S.—is underway and is expected to be completed sometime in 2018, according to the California Department of Water Resources. The dam replaces the previous spillway, which was damaged by heavy flooding in February.
Problems at the Oroville Dam began, when the dam’s main sluice was damaged after a winter season of record rain and snowfall, following five years of drought. Torrential rainfall caused water levels to rise so quickly that large amounts needed to be released to prevent the dam from rupturing and sending a wall of water to the communities below.
The force of the cascading water was so strong that it created a large hole in the main sluice, requiring the use of an emergency spillway. This safety backup, however, also nearly failed because the dirt spillway, which had never been fortified by concrete, began to erode, increasing the risk of damage to the dam. In anticipation of a possible disaster, almost 200,000 residents living below the dam were temporarily evacuated.
The dam’s new construction has proved to be contentious at times, with residents expressing concern about small cracks that have appeared in the freshly laid concrete. Rainy season is just ahead and residents are anxious about the possibility of another flood.