U.S. Army Corps of Engineers says Whittier Narrows Dam is unsafe and could trigger catastrophic flooding
Federal authorities are particularly concerned that an extreme storm could trigger premature opening of the dam's massive spillway, which is designed to open automatically when a pool of water behind it rises above 228.5 feet in elevation.
"Under certain conditions, the spillway on the San Gabriel River can release more than 20 times what the downstream channel san safely contain within its levees," according to an Army Corps report. "Depending on the size of the discharge, flooding could extend from Pico Rivera, immediately downstream of the dam, to Long Beach."
Greg Fuderer, a spokesman for the Army Corps' Los Angeles District, said construction of projects designed to reduce the likelihood of failure is expected to begin in 2021.
"Until all of these issues are ironed out," Fuderer said, "we cannot approve any sort of construction project in the flood plain."
The hold on construction could bring an end to a 20-year struggle to build a proposed 14,000-square-foot Discovery Center in a wildlife sanctuary near the dam, about 12 miles east of Los Angeles and about 30 miles south of the river's headwaters in the San Gabriel Mountains.