During the winters of 1996-1997 and 1997-1998, a dedicated effort to make winter releases at higher rates was attempted. This involved not only increasing the winter release rate but additional vigilance, so that flooding situations could be avoided. While it appears obvious that it would be beneficial to almost everyone to make higher releases during the winter it is not that simple. During this 1996-1997, winter releases were at record levels but caused problems. During the winter when an ice cover forms on a river channel the stage is increased dramatically over open channel conditions because of the additional friction caused by the rough ice cover. If release increases are scheduled slowly after a freeze-in, the dramatic rise can be reduced but this takes both time and vigilance to increase at the correct rate to not cause downstream flooding. Also at times, the channel becomes blocked by ice action and you simply cannot get the water to the next dam downstream. This applies for all the river reaches between the dams. Gavins Point dam can be totally drained in a few days if the water is not continually moving into it. The water not making its way to the dam, basically spreads out upstream of the dam and floods. Also experience during 1996 would indicate that ice bridging situations can be made worse by higher flows. During 1996 despite higher release rates, Sioux City reached a record low stage during an ice bridge event in January. This was because the higher flows caused the ice to bridge more, which resulted an increased restriction and less flows passing downstream. Above the ice bridge, stages increased dramatically, the ice bridge fortunately was in a reach that could handle the increased river levels with no physical damage to property next to the river. If this would have happened below a major urban area or housing area a significant amount of flood damage could have occurred.
One should also realize that almost all tributary flow is very low during the winter because those streams are frozen completely. So even if the releases are increased significantly, the river is still going to look very low downstream, except where it is frozen over, because of little or no tributary flow. Without the dams, the rivers were always very low during the winter freeze-in period, so it is not natural for the river channels to carry higher flows during the winter months when ice is forming on the river. To increase releases during this period takes away the natural buffer of the space in the channel to handle the dramatic rises that could occur. While these rises may not cause significant damage in rural areas, the urban reaches could be significantly affected if a bridge were to occur immediately downstream with the higher flow rates and reduced channel space.
So when deemed necessary, the Missouri River Water Management Division will make winter releases at the higher rates and closely monitor the situation so adverse affects are minimized.