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, Jan. 7, on Missouri River basin management.

John Remus, chief of the Corps’ Missouri River Basin Water Management Division, said that Gavins Point releases would be increased from 27,000 to 30,000 cubic feet per second in the following week. Gavins Point Dam, located on the southeast South Dakota-northeast Nebraska border, releases normally range between 12,000 and 17,000 cfs in the winter.

“The higher-than-average winter releases from Gavins Point will continue to empty stored water from the 2019 runoff season,” Remus said.

Remus said December runoff in the Missouri River basin 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.

Snowpack projections

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 Jan. 13.

For now, said Corps officials, total snowpack in the Upper Midwest is slightly above normal, but they pointed out that we are not even at the halfway point of the snow accumulation season. Mountain snowpack typically peaks in April. Plains snowpack is currently greater than at this time last year.

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. One slide showed a current baseline of 56.6 million acre feet storage, slightly above the baseline of 56.1 maf.

Levee repairs proceeding

Both the Omaha Engineer District and Kansas City Engineer District are proceeding with repairs of levees breached or damaged by the floods of 2019. Matt Krajewski of the Readiness Branch of the Omaha district reported that 21 levee breaches have been closed in the Omaha district, including several over the weekend. A very important breach at the confluence of the Platte and Missouri rivers that led to a new channel was closed.

The Kansas City District recorded 279 consecutive days of “above normal” operations, a record.

In response to a question, Krajewski said levee repairs are proceeding faster in the Omaha District because it has a higher proportion of purely federal levees, whose repair is 100% funded by the Corps. Kansas and Missouri, by contrast, have more levees whose upkeep costs are shared with local levee boards and districts. The cost-share is typically 80/20, which means that consultations have to be undertaken with local levee boards before work can begin, and in some cases to allow local levee boards to raise funds.

David Murray can be reached at [email protected].