July 19, 2017
IT WAS A SUNDAY EVENING in February when residents of three counties in Northern California were ordered to evacuate their homes in the Feather River Basin. After heavy rainstorms doused the region, the Oroville Reservoir was at capacity, and excess water was sent out over the primary spillway and down the Feather River. Soon, dam operators with the California Department of Water Resources (DWR) noticed a crater had formed in the spillway. The Oroville Dam, the tallest in the United States at 770 feet, was stable, but the spillway was an important part of the reservoir’s flood control system. Soon, the bottom half of the concrete chute had crumbled, sending debris into the river and forcing the DWR to use another, emergency spillway for the first time. But the massive flows eroded that earthen path as well. If the erosion had continued and undermined the concrete lip of the spillway, a massive flood would have swept down the river into the valley below—a 30-foot wave of destruction.