Nebraska dam had history of ice woes before fatal failure
A Nebraska dam that collapsed under pressure from an icy flood had a history of unaddressed ice problems and had no formal emergency plan because regulators wrongly assumed that no one would die if it failed, according a report released Tuesday.
However, the investigation concluded there was nothing the dam’s operators could have done in the early morning of March 14, 2019, to prevent Spencer Dam from failing after an unusually intense storm created a raging flood of ice chunks on the Niobrara River in rural northern Nebraska.
Kenny Angel, who lived just beneath the dam, died when the flood washed away his home and business. Workers for the Nebraska Public Power District, which operated the dam, warned Angel just minutes ahead of time of the impending danger but fled without him.
The failed hydroelectric dam was featured in an Associated Press investigation in November that found scores of dams nationwide in even worse condition, and in equally dangerous locations. The AP identified 1,688 high-hazard dams — meaning loss of life is likely if they fail — rated in poor or unsatisfactory condition as of last year in 44 states and Puerto Rico.
Nebraska regulators had categorized Spencer Dam as a “significant hazard” — a rating that meant no loss of life was expected if it failed, and no formal emergency action plan was required. Tuesday’s report by the Association of State Dam Safety Officials said the dam should have been rated as “high hazard,” which could have led to a plan to increase its flood capacity and provide better warning to downstream residents.
The dam’s hazard rating dated to the 1970s and hadn’t undergone a comprehensive re-evaluation using newer techniques, the report said.
Nebraska’s chief dam safety engineer, Tim Gokie, defended the classification. He said multiple engineers and organizations had reviewed it over the years and rated it as anywhere from low to significant hazard.
Mark Becker, a spokesman for the Nebraska Public Power District, said staff members were reviewing the report and had no immediate comment.
The report cited the wrong classification as one of two human factors contributing to the dam’s failure and devastating consequences. It said state regulators were unaware the dam had failed under ice pressure in March 1935 and been damaged by ice on the river in March 1960 and March 1966.
The past ice incidents “could have been warning signs to the dam owner and regulator,” the report said, but historical records about the dam were lost, unorganized or unavailable.
Gokie said the state office has only limited information on dams before 1967, when it began routine inspections.
State inspections of Spencer Dam were done in the warm-weather months, when there was no ice on the river, and focused only on observable deficiencies, not less-visible vulnerabilities, the report said.
As a result, “while the dam appeared to be well maintained, no provisions were made to pass or prepare for ice run events,” the report said.
After its 1935 failure, the dam was rebuilt in 1940 in a way that actually made it harder to pass ice chunks through its nine, 33-foot (10-meter) wide flood gates, the report said. That was problematic because the Niobrara River is especially prone to large ice flows.
Mark Baker, the leader of the panel that produced the report, said the failure of Spencer Dam has lessons for other dams, especially those in colder climates.
“If you are in charge of inspecting or evaluating the safety of any dam in cold weather regions, you need to screen for whether ice runs are a potential there and could damage your dams,” said Baker, who heads a dam consulting company in Denver.
“We have known for a long time that ice can put pressure on dams. Ice can squeeze up against a gate and keep it from opening,” he said. “But this idea that the chunks can come down in the thousands in rivers and cause overtopping flows is a new concept.”
Baker also said safety engineers need to go beyond simply inspecting dams and start looking at their history, how they were constructed and how they would performs in a disaster.