Nebraska Flood Exposes Weak Points
Officials from the U.S. Army Corps of Engineers, the Nebraska Dept. of Natural Resources, the state’s biggest public power utility and local fire departments were all overwhelmed by a combination of frozen ground, rain and snow in mid-March. The Platte and Missouri river systems could not drain the inundation, and it didn’t help that much of the infrastructure in place wasn’t ready for such a combined storm and cold event.
“The snow amount and the rainfall totals were not uncommon; what was uncommon for us was that one happened on top of the other,” says Tim Gokie, dam safety chief for the Nebraska Dept. of Natural Resources (NDNR), the state agency in charge of inspecting the state’s 2,924 dams.
Gokie says it’s too early to draw any conclusions, but he added that when evaluating critical or high-risk infrastructure in places that see snow, engineers need to think about rain on snow on frozen ground with zero infiltration.
“Like most of the nation’s infrastructure, our dams are aging,” Gokie says. “Many of the dams were designed with a 50-year design life. We have 1,200 dams in our inventory that are more than 50 years old. Repairs and upgrades to dams are expensive. It can be a real struggle for both public and private dam owners to find funding to make upgrades.”
Flood damage in Nebraska stood at $1.3 billion on April 1. The total includes $449 million in damage to roads, dams, levees and other infrastructure, $440 million in crop losses and $400 million in cattle losses. President Donald Trump, through the Federal Emergency Management Agency, announced March 21 that federal disaster assistance was available to the state.
Three deaths have been confirmed so far. A widely publicized symbol of the devastation is the U.S. Highway 281 bridge between the small northeast Nebraska towns of O’Neill and Spencer, swept away when the 92-year-old Spencer Dam, just upstream of it, was breached and destroyed on March 14.
Kenny Angel, a 71-year-old resident who lived just below the dam and managed a campground near his home, is presumed dead after the campground and his house were destroyed by flooding on the Niobrara River after Spencer Dam was breached. Part of the Highway 281 bridge remains on the Spencer side, but the entire bank on the O’Neill side of the bridge has been cut away by chunks of ice and high water, creating a new, clifflike bank and stripping away the roadway that once led to the bridge. Spencer Dam, owned by the Nebraska Public Power District, was a 3,700-ft-long hydroelectric dam that consisted of a 400-ft-long gated spillway section and powerhouse, and a 3,300-ft-long earthen dam embankment.
The main failure was not at the gated spillway structure. While several of the gates were destroyed, the main breach occurred toward the south end of the earthen dam embankment, according to Gokie. NPPD said that its personnel tried to open tainter gates on the dam but some were frozen shut by the ice and cold water.
The last two supervisors on site abandoned the dam only after it became obvious that the earthen part of it was failing.
The bridge had last been inspected in April 2018. The Dept. of Natural Resources identified four issues during that inspection. Gokie called three of them minor maintenance issues. The fourth was an area of seepage below the dam. NPPD had taken steps to address the seepage with a new drain system in 2015. “We recommended they monitor the seepage area,” Gokie says. “Based on what we currently know, it is doubtful [that] embankment seepage played any role in the failure.”
NPPD had agreed to sell the water rights to the dam to the Nebraska Parks and Game Commission in 2018, but the transaction never closed because the commission never completed the purchase, according to NPPD spokesman Mark Becker. It was still operating as a hydroelectric power dam the week before its collapse and, Becker says. NPPD will retain the water rights. No decision has been made on whether to keep or demolish what remains of the dam.
“There needs to be a better understanding of what this facility was intended to be,” Becker says. “A lot of people, their thought was: Wasn’t this supposed to control flooding? When it was built in the ’20s, it was never ever designed to do that. It’s a run-of-the-river hydroelectric facility, and not a flood control operation. We’ve seen claims out there of an 11-ft-tall wall of water. Right now, we are actually looking, gathering all of the information so we have a better understanding of what the situation was at the time.”
Indeed, much of dam and levee infrastructure in southern Nebraska was not designed for flood control. Many of the communities in the area have focused on securing scarce water in the summer months rather than on flood control. Only four of the six reservoirs on the Missouri River operated by the U.S. Army Corps of Engineers are designed to impound significant runoff. The runoff from this flood event happened downstream of all four of those high-capacity reservoirs.
The dam and reservoir system that serves southern Nebraska had 22% of its space set aside for flood storage, and 96% of that stood empty and ready to take in water before the flood events the week of March 10. Unfortunately, much of the water that flows down the Niobrara River into the Missouri ends up at the Gavins Point Dam on the Nebraska-South Dakota border. The Lewis and Clark Lake it creates is the only place to deposit water near Gavins Point. It has capacity to hold back less than 1% of the water in those six reservoirs. The Corps had little choice but to open up its floodgates. The lake rose 1.6-feet higher than it ever had before. Water that was equivalent to 31 times the river’s average March flow poured into the lake. Further downstream, the Platte River dumped more water into the Missouri, swelling it to record levels. South of the Platte, levees quickly overtopped—some failed and others were structurally compromised. Beyond dams and reservoirs, wastewater and freshwater processing plants near all of southern Nebraska’s rivers announced emergency shutdowns.
The Corps’ mission, as defined by Congress, is to manage the Missouri under eight priorities; flood control is one of only one of them. Others include hydroelectric power, endangered species and recreation.
“When we talk about water resiliency west of the Missouri River, we always talk about not enough water, right?” says John Mitchell, director of alternative delivery at Burns & McDonnell. “We’re focused so much on water resiliency being drought resiliency.”
In Spencer, Shawn Davis, chief of the volunteer fire department who was in charge of the first response to the dam and bridge collapse, is now dealing with a community that has no water. Rural Water District 2, which covers Boyd County, saw its 12-in. water-supply main, which connects its four groundwater wells and a main storage tank north of the Niobrara, destroyed with the highway and dam.
The community is trying to raise $400,000 as its part of the $1.073 million cost of replacing the water line. The district will be working with FEMA, but is responsible for its portion of the project. The district also must pay for new costs, such as trucking in water for residents until the new line is built. Horizontal of Exeter, Neb., won the emergency design contract for the new water line.
“Everything in the Niobrara Valley south of the dam and the bridge is gone,” Davis says. “It’s going to take some time to get back to anything close to normal.”