SPENCER — The state’s top dam safety official says that huge chunks of ice — some weighing as much as a full-sized pickup — played a leading role in the collapse of northern Nebraska’s Spencer Dam.
Tim Gokie, chief engineer of the state’s dam safety program, said it may be the first dam failure in the nation related to ice floes. That ice, carried by epic floodwaters, most likely caused the 92-year-old concrete-and-earthen dam to wash out last month, rather than age or any deficiencies identified in state inspections.
“With age comes problems with any infrastructure — steel corrodes, concrete deteriorates over time,” Gokie said. “But there’s no indication that any of that led to the failure of the dam.”
The collapse of the 29-foot-high dam unleashed a wall of water 11 to 15 feet in height, washing away a home, several trailers and a unique straw-bale saloon/bait shop just below it. The body of Kenny Angel, who lived in the home, has yet to be found amid the debris and ice chucks cast downstream.
His siblings filed a legal claim last week with the owner of the dam, the Nebraska Public Power District, for his loss of their brother and the saloon, which had been owned by the Angel family for more than 50 years. The claim is a precursor to a likely lawsuit against the public utility, which has said its employees had warned Angel to evacuate immediately moments before the dam collapsed.
His family maintains that Angel wasn’t given enough warning and that “appropriate steps were not taken to mitigate against the risk of the present calamity,” said their attorney, Mike Coyle of Omaha.
The area around Spencer Dam is a virtual wasteland of sand and debris now. The skeleton of the concrete portion of the structure, along with the vast fields of sand, has become one of the iconic images of the 2019 flooding.
The earthen section of the 3,700-foot-long dam now has two huge gashes. A new channel of the Niobrara River was created by the flood, which washed away about a quarter-mile of U.S. Highway 281. The state is now considering the use of a temporary bridge to restore traffic on the highway, which serves as a major connection between O’Neill and Holt County on the south, and Boyd County on the north.
While NPPD continues to investigate the dam failure, what’s clear is that on the night of March 13-14 an epic amount of water and ice had built up behind the dam — which state inspection records have regularly labeled “well-maintained” over the past 25 years.
Flows in the Niobrara River just below the dam measured up to 40,000 cubic feet per second, which was about 27 times the normal flow of 1,500 cubic feet per second, just before the dam failed, according to Jason Lambrecht, who collects hydrologic data for the U.S. Geological Survey in Lincoln.
Ice on the river measured 18 inches to 24 inches thick before the collapse, which came amid a local blizzard followed by more than 2 inches of rain. Lambrecht said that based on the size of the ice chunks found after the collapse, some weighed as much as 3 tons.
“When you add that ice in the mix, it can be really destructive,” he said. He added that a final calculation of the flood flow, which has been complicated by the destruction of river gauges, is not expected for another month.
NPPD officials have said their workers abandoned the dam after unsuccessfully trying to open more floodgates and noticing that water was beginning to overtop the earthen portion of the structure. The workers, they said, immediately drove to Angel’s house, told him to “get out now” and then drove away.
Boyd County residents have numerous theories as to why Angel didn’t get away: Maybe he was groggy and moving slowly at 5:30 a.m. after working at the family bar until 2 a.m.; maybe he tried to retrieve his wife’s dogs that were still in the house (she was out of town at the time); maybe he was in the process of driving away when the water and ice hit.
Mark Becker, an NPPD spokesman, said last week that the utility is still working on its internal review of the collapse.
“Our initial look was we had an unprecedented amount of water, combined with the ice,” Becker said.
Gokie, who heads the dam safety program at the Nebraska Department of Natural Resources, said he could not say exactly what caused the dam to fail, but he said it was very clear that “the flood exceeded what the dam was designed to handle.”
When water began pouring over the top of the earthen portion of the dam, it was an alarming sign. About 34% of all U.S. dam failures are caused by water overtopping a dam, according to the national Association of State Dam Safety Officials. Overtopping, the safety group said, is usually caused by blockages of spillways or inadequate spillways.
Gokie added that ice jams and ice floes are not generally considered when judging the relative safety of a dam.
The World-Herald reviewed 25 years’ worth of state inspections of the dam. The inspections — which were conducted every two to three years — regularly suggested some repairs, but also commonly described the dam as “well-kept” and described recent improvements, including new “rip-rap” installed to deal with erosion on the dam and extensive concrete work done in the spillway area in 1999.
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Jay Lund, a geology and hydrology professor at University of California, Davis who led a study of the 2017 near-failure of the spillways at the Oroville (California) Dam, said inspections can show a pattern of problems that, if unaddressed, can lead to catastrophe.
Lund said that conditions were ripe for flooding in Nebraska, with a combination of high precipitation, snow cover and frozen soil, but that “Dam Safety 101” is to design for “the probable maximum flood.”
“You want to have a spillway that will pass (floodwaters),” he said, adding that poor design and poor maintenance usually are the culprits in a dam failure.
But Gokie, the state inspector, said his look at past inspections of the Spencer Dam did not show repeat problems that went unaddressed. NPPD, he said, regularly responded when deficiencies were found.
“I would definitely say that we have dams that are not well-maintained, but this was not one of them,” Gokie said.
Exposed rebar and cracking and spalling of concrete were regularly noted in the spillway of the dam, but those problems do not contribute to a dam collapse, he said. The spillway area remained intact after the flood.
“Seepage” through the earthen portion of the dam was noted during inspections in 1999, 2008 and 2012, but Gokie said such seepage is normal in an earthen dam. NPPD responded by installing a “very extensive” system of “toe drains” to siphon the seepage away, which he said is the correct response.
Only once — after an inspection on Sept. 10, 2008, found bubbles rising in water just upriver from the dam — did a state inspector “strongly recommend” close monitoring and that an engineer take a look.
NPPD responded by draining the dam. An Oct. 8, 2008, memo said a large log had been found in the area of the bubbles. Gokie said that was the probable cause of the bubbles. Six months later, an inspection noted that the bubbles had dissipated, adding, “Overall, the Spencer hydro dam is a well-kept structure.”
State inspectors gave two ratings for Spencer Dam. One was that it posed a “significant” risk for causing damage in the event of failure. Gokie said that was because it was a large dam that had homes and property below it.
Most large dams in the state get a “high” rating, the next-highest rating, he said, because of their size. But many of the flood-control dams in the Omaha area are also rated at “high” risk for potential damage because of the hundreds of homes and businesses below them.
The Spencer Dam got a “fair” rating for its condition, which came with an ominous warning: “deficiencies exist which could lead to dam failure during rare, extreme storm events.” But Becker, the NPPD spokesman, pointed out that such a rating also comes with the condition that “acceptable performance is expected under most conditions. ...”
The grim search for Kenny Angel continued over the weekend, with helicopters and drones flying up and down the Niobrara, which still has large fields of ice chunks and debris along the banks. Members of his family, law enforcement and others walked the banks of the river.
At ranches along the river, preparations were being made to bury dead cattle. At nearby Lynch, the local convenience store was to reopen this week after floodwaters swamped that community of 245.
And at the road-closed signs blocking access to the washed-out highway below the Spencer Dam, small groups of sightseers gazed up at the old structure and the sandy moonscape where Angel’s Straw-Bale Saloon and Kenny Angel’s home once stood. Many shook their heads.
The only sign that a popular gathering spot once stood there is a flagpole, planted by Angel’s family, that is flying the American and Nebraska flags.