Soaked Soils Make Missouri River Floods More Likely
The record floods of 2019 left Upper Midwest soils so super-saturated that even a modest increase in winter precipitation and runoff could threaten another record flood season on the Missouri River in 2020.
The Ohio River and Lower Mississippi River valleys are expected to get higher than normal precipitation this spring.
Those were among the take-away messages from a webinar /conference call given by the Corps of Engineers January 7 on Missouri River management for the coming season.
John Remus, chief of the Corps’ Missouri River Basin Water Management Division, said that Gavins Point releases would be increased from 27,000 cubic feet per second (cfs.) to 30,000 cfs. in the following week. Gavins Point Dam winter releases normally range between 12,000 and 17,000 cfs. “The higher-than-average winter releases from Gavins Point will continue to empty stored water from the 2019 runoff season,” Remus said.
Remus said the December runoff was three times the average and the highest on record. Corps hydrologist Kevin Lau noted that 2019 was the second-wettest year in the Missouri River basin since records were kept, except 1993. One slide showed that soils in the region are still in the upper 99th percentile of moisture. Kevin Grody, reservoir regulation team lead for the Corps’ Missouri River Basin Water Management team, said January and February runoff could be twice normal,
For now, said Corps officials, total snowpack in the upper Midwest is slightly above normal, but they pointed out that it is not even at the halfway point of the snow accumulation season. Mountain snowpack typically peaks in April.
The navigation service level is determined by the amount of storage in the controlling reservoirs on March 15, which Grody said would likely be higher than average this year.
Colder than normal temperatures are expected from January through March, along with higher than normal precipitation—but Corps officials added that those forecasts came with some uncertainty, since there is no El Niño or La Niña weather system driving weather this year.
Lau said snowpack conditions were near normal in most locations in the Missouri River basin, above normal in a few places, but “much could change” in the coming weeks. The 90-day river outlook forecasts a high probability of flooding in several tributaries of the Missouri River. The National Weather Service was due to issue an official spring flood outlook January 13.