News Release
June 5, 2011 Update

Coalition urges support for flood victims
The current extreme water runoff from a year of major snow and rainfall is forcing water releases from the Missouri River dams that have never before been experienced, resulting in flooding in many areas. While flood control was one of the major benefits of the dams when they were constructed, dams and levees can never eliminate all flooding risks. One of the problems contributing to the flooding problem is sediment accumulation in the reservoirs.

Since its creation, the Missouri River reservoir system has lost over five million acre feet of storage due to accumulating sediment. According to a recent Sioux Falls Argus Leader report, the Missouri River system has a storage capacity of 73.1 million acre feet. The system was at 68.5 million acre feet on Friday May 27, according to the report.

This lost storage is the equivalent of a flood one hundred miles long, ten miles wide, with an average depth of over seven feet, according to Howard Paul, technical coordinator with the Missouri Sedimentation Action Coalition.

"That is a major flood, but the current run off would still create problems. Sediment causes another problem that is a major contributor to the flooding and damages we are now experiencing," Paul said.

As sediment enters the reservoirs from flowing streams, that sediment drops out when the flow enters the still waters of the reservoirs. These sediment deposits create a damming effect within the reservoir itself, and this damming effect causes the inflowing water to have to flow over these dams, thus raising the surface elevation of the river. This takes place both downstream and upstream of the point of inflow and raises the ground water table in the soils adjacent to the river.

"As this sediment build up continues, the effects continue to multiply. The situation in south east Pierre and in areas of Fort Pierre, South Dakota, where higher and higher ground water tables forced the ‘buy-out’ of hundreds of homes is a proven example of this situation," Paul said.

Paul added that another was the confluence of the Niobrara River and the Missouri River at Niobrara, Nebraska. Other areas are facing this same problem on an increasing scale.

"This situation will only worsen in time without sediment management. We are experiencing a very unusual event with the amount of snowpack coupled with the amount of rainfall. What is happening also magnifies the sediment problem. It cannot be ignored. We must remember a perfect reservoir system cannot prevent all flooding all the time, everywhere on the system," said Sandra Korkow, MSAC executive director. "However, sediment management will go a long way to lessening harmful impacts felt up and down the river."

The system must be kept in tune to maximize its lifespan and functions. Unattended sediment entry into the reservoirs puts a preventable strain on the system, which unnecessarily complicates management, she said. Employing sediment management will be costly in the short-term, but it is a necessary component of keeping the system healthy and sound financially in the long-term.

Dredging or moving sediment downstream of the dams and reducing the amount of sediment entering the reservoirs will not prevent all future flooding. It will benefit the ground water table levels and free up storage capacity to hold more water. Sediment management will work to decrease the negative impacts felt up and down the Missouri River, however man cannot eliminate all the harsh elements produced by Mother Nature.

"Sediment management may not prevent all the flooding currently being experienced in places like Bismarck/Mandan, Pierre/Fort Pierre, the Niobrara area, Yankton, and the length downstream of Sioux City," said Korkow. "We do know that without moving sediment and keeping sediment from the reservoirs this situation will worsen and smaller flood events will continue to grow in severity especially near tributary deltas."

Without the Missouri River dams, flooding would be much worse and Americans would not enjoy hydropower, a prime drinking water source, irrigation supplies, and expanded recreation. "We must keep this investment running smoothly and invest to maintain it," Korkow said.

This is a very crucial time for many areas up and down the Missouri River as people are working tirelessly in efforts to combat the flooding. This is a very serious disaster for thousands of people, stated Korkow.

"MSAC does not want to shift the focus of what needs to be done here and now to fight the flooding. The discussion of the need for sediment management is not diminishing but grows each day," Korkow said.

● Photo Below: Niobrara Railroad Bridge on May 30, 2011 (MSAC Photo)

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Follow this link to a PDF version of our June newsletter.  Pages 1, 2, 5, 6          Pages 3 & 4

Howard Paul, technical coordinator email: hpaul@sio.midco.net
1511 Holiday Drive
Canton, SD 57013 (605)987-4165 (605)770-0998