Tens of thousands of large dams across the globe are reaching the end of their expected lifespans, leading to a dramatic rise in failures and collapses, a new UN study finds. These deteriorating structures pose a serious threat to hundreds of millions of people living downstream…. In 2017, a spillway collapsed at the 50-year-old Oroville Dam in California’s Sierra Nevada foothills. It caused the evacuation of around 180,000 people. The 770-foot dam is the highest in the U.S. and, after repairs to the spillway, remains critical to the state’s water supply.