We know sediment accumulates in our Missouri River reservoirs at a rate of about 89,700 acre feet per year. We lose storage of enough water, each year, to supply more than 800,000 people with 100 gallons per day for an entire year. We already have lost enough space to store a flood equivalent to 100 miles long, 10 miles wide, with an average depth of 7 ½ feet. In 2010, we were quickly reminded how important this capability is for people in numerous states. Flooding caused by inflow from tributaries below Gavins Point Dam would have been much worse if the Missouri River dams would not have been able to hold and store runoff water from within and above the System.
Prior to dam construction, the river carried heavy loads of silt, gathered from tributary streams and bank and bed erosion in the river itself. The tributary streams and the river had enough velocity to carry the sediment, only depositing it in still waters, of which there were not many. Once the dams were constructed, the river became a series of free flowing rivers interspersed with dams and their reservoirs. Once the sediment carried by the tributaries and by the river through bank and bed erosion hit the still waters of the reservoirs, it dropped out to form deltas. These deltas create a damming effect at the entry point into the reservoirs, which causes a rise in the level of the ground water in adjoining lands. This increased ground water causes damages to property, such as flooding root zones of cropland, flooding basements, damaging roads and other facilities to name a few.
Some researchers call the reservoirs "sediment traps." Sediment is needed downstream of the Missouri River dams for a variety of reasons, including sandbar habitat for threatened and endangered species. MSAC supports reducing the amount of sediment entering the system through sound land management. MSAC also supports managing and removing sediment from the reservoirs in order to sustain the valuable benefits created by the Missouri River reservoir system.
(MSAC Photo 2007 The Niobrara river enters the Missouri river near niobrara, nebraska, upstream of lewis and clark lake created by gavins point dam at Yankton, south dakota)
Learn more about the benefits produced by the Missouri river reservoir system
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