The spring flood risk, which is higher than normal across the region, is especially high along the Missouri River, federal officials said Thursday.
The U.S. Army Corps of Engineers, which manages six massive dams on the Missouri River, and the National Weather Service, which forecasts flooding, voiced shared concerns Thursday during a monthly update: Soils are overly wet, rivers are running high and the weather could throw some wild cards into the mix.
In January, runoff into the Missouri River was nearly double normal, said Kevin Grode of the corps’ Omaha District. That’s an indication, he said, of how saturated soils remain. Soil moisture readings rank in the 99th percentile in many areas.
“Generally when soil moisture is high during the winter, the potential for high March and April runoff is much higher,” said Grode, who is team lead for reservoir regulation.
The corps is forecasting 2020 to be among the top ten runoff years in 122 years of records, said John Remus, chief of the corps’ Missouri River Basin Water Management. The agency is estimating that runoff will be about 141% of average and rank ninth highest.
Remus said the agency has been moving aggressively to release water from its reservoirs so it has more flexibility on setting release rates as snow cover melts and spring rains arrive. The corps this week increased releases from Gavins Point Dam to 35,000 cubic feet per second, up from 30,000 cubic feet per second. Releases now are running at more than double average for this time of year.
Particularly worrisome is heavy snow cover in the eastern Dakotas. Contained in that snow is 2 to 3 inches of water, said Kevin Low, a hydrologist with the weather service.
The soil beneath that snow is saturated, so snowmelt will largely run off instead of soaking in. As an indication of how waterlogged that area is, Low pointed to the James River. It has been above flood stage for 329 consecutive days, he said. The James is among the tributaries that feed into the Missouri River below the dams, which means there’s no way for the corps to hold back its flows.
“Springtime flooding guaranteed,” Low said.
Runoff from that snowy area could be three to five times average, Remus has said, which is one reason the corps is evacuating as much water as possible from the reservoirs.
The potential for above-normal runoff and already high levels of rivers that feed into the Missouri below the dams are the reasons the officials are especially concerned about the Missouri River.
The risk along the Missouri is highest downstream of Omaha. Remus encouraged people to monitor weather service forecasts, set up weather alerts and check river stages daily.
Also of concern is the long-term outlook for the last half of February to turn colder than normal and possibly snowier than average.
Because rivers are running high and sharply colder weather is possible, Low said the region has “an especially high likelihood” of ice jams.”