October runoff into the Missouri River basin above Sioux City, Iowa, was 2.8 million acre feet (MAF), more than two times normal and the second highest October runoff since recordkeeping began in 1898. October runoff in the Oahe and Fort Randall reaches were the first and second highest on record, respectively. As a result, the updated forecast for 2013 runoff is 25.9 MAF, 102 percent of normal. Normal annual runoff is 25.2 MAF.
“The upper basin has experienced a wet fall this year, with above normal rain and heavy snow in some areas in early October. This has resulted in wet soil conditions across much of Montana, Wyoming and the Dakotas,” said Mike Swenson, team leader in the Missouri River Basin Water Management office.
Due to the higher runoff, the total volume of water stored in the Missouri River Mainstem Reservoir System increased 0.4 MAF during October. “Despite 2013 runoff being normal, the impacts of the 2012 drought are still being felt at the largest three reservoirs - Fort Peck, Garrison, and Oahe. These three reservoirs are currently drawn down 3 to 10 feet below their desired levels,” said Swenson. “Our long-term studies indicate that we will likely begin the 2014 runoff season with system storage 4.6 MAF below the base of the annual flood control and multiple use zone.” The annual flood control pool is the desired operating zone for the system because it allows the Corps to fully serve all eight congressionally authorized purposes.
“We will be paying close attention to the amount of mountain snowpack we receive in Montana and Wyoming as well as the plains snow accumulation in the Dakotas, this winter,” said Swenson. “We will know more about the potential impacts of the wet fall basin conditions by the start of the 2014 runoff season when we can factor actual on-the-ground conditions into our forecast models and we will include that information in our decision-making process.”