|Dams ranked by hazard (FEMA map; click on the image for a larger version)|
Nearly 200,000 people were evacuated downstream in early February 2017 when engineers discovered damage to the spillways after heavy rains. Repair of the dam is estimated to cost $500 million. The dam was inspected regularly before the disaster, but in the interim report released Sept. 5, investigators said the inspectors relied too heavily on visual inspections. "Due to the unrecognized inherent vulnerability of the design and as-constructed conditions and the chute slab deterioration, the spillway chute slab failure, although inevitable, was unexpected," the panel report said.
The investigators also warned the entire dam industry to pay attention, since about 14,000 of the more than 87,000 dams in the U.S. are classified as "high hazard potential".