Mo Basin Faces Above Average Runoff

Corps of Engineers Forecasts Runoff at 35.5 Million Acre Feet

Todd Neeley
By  Todd Neeley , DTN Environmental Editor
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Although runoff in the Missouri River basin is expected to be much less in 2020 than it was in 2019 and 2011, officials with the U.S. Army Corps of Engineers cautioned basin residents to continue to watch flood forecasts. (DTN photo by Elaine Shein)

OMAHA (DTN) -- Though the 2020 annual runoff season in the Missouri River basin is expected to be nowhere near the record levels of 2011 and 2019, officials with the U.S. Army Corps of Engineers and the National Weather Service do expect above-normal runoff this year.

During a call with basin stakeholders and media Friday, Corps officials wanted to make sure those living in the basin do not take their eyes off the flood threat while social distancing during the COVID-19 outbreak.

Kevin Low of the National Weather Service's Missouri Basin River Forecast Center said, mountain snowpack is close to the seasonal peak accumulation date in the basin.

Soil moisture conditions have improved as most of the winter snowmelt has occurred in much of the region.

However, Low said soil moisture conditions remain abnormally high, providing an enhanced flood risk across the eastern portion of the basin.

Throughout March, flooding has been seen along the Milk River, James River and Little Sioux River, as well as along several tributaries in Missouri, including along the Grand and Osage rivers, Low said.

The Missouri River already has experienced flooding from Nebraska City, Nebraska, to the mouth of the river.

Low said the lower basin will see flooding going into early summer as thunderstorm activity increases.

The Corps of Engineers forecasted annual runoff in the upper basin this year at 35.5 million-acre feet as of April 1, or about 138% of the average. Last year, basin runoff topped 60 million-acre feet (MAF), as it did in 2011. The average annual runoff for the upper basin is 25.8 MAF.

The Corps of Engineers reduced its March 1 forecast by 1.4 MAF, in the latest update.

The latest forecast still is in the top 10% of the 122 years of runoff records, according to the Corps of Engineers.

As of April 8, system storage was 58.6 MAF. In addition, about 85% of flood control storage is available to account for spring rainfall events.

According to a Corps of Engineers' news release, releases from Gavins Point Dam in South Dakota are forecast at around 35,000 cubic feet per second through the end of April.

Basin runoff in March came in as forecasted, according to the Corps of Engineers, at 5.5 million-acre feet above Sioux City, Iowa, or about two times average runoff because of melting snow on saturated soil in the Plains.

The Corps of Engineers said there are above-average chances of precipitation for the basin from April to June, while equal chances of below- or above-normal precipitation from July to September.

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Todd Neeley

Todd Neeley
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