Escalating Floods Putting Mississippi River’s Old River Control Structure at Risk

Above: The Old River Control Structure on the Mississippi River as seen during a flood on May 17, 2009 (left) and at normal waters levels on December 31, 2009 (right).

Weather Underground paints uplifting article on Mississippi River ORCS


Figure 3. Landsat image of the Mississippi River, showing the location of the Old River Control Structure (ORCS) and Widow Graham Bend, located 13 miles to the north-northwest of the ORCS. If the Mississippi broke through its west bank levee at Widow Graham Bend, it could cut a new path to the Gulf of Mexico via the Red River and Atchafalaya River.

"Danger from sandbars upstream
River engineering has forced the river to dump a massive amount of sand upstream from the ORCS. A total of 30 large sandbars containing about 530 million tons of sediment have formed along a 100-mile stretch of the river upstream from the ORCS since 1985 (Figure 2). Future floods could dislodge that sand and wash it downstream, where it would raise the river bottom just south of the control structure, increasing the plugging effect and boosting flood heights to even more dangerous levels.

Major floods can also wash a large amount of sediment into the control structures, threatening to completely block them. A 2011 study, Mississippi River and Old River Control Complex Sedimentation Investigation and HSR Model Report, warned that “there is a real possibility and threat that both Low Sill and Auxiliary could become totally buried with sediment during an extreme event,” leaving only the hydropower structure to manage the flow between the Mississippi River and the Atchafalaya River.

The great flood of 2011, the highest flood ever recorded on the Lower Mississippi River, carried a large amount of sediment into the Low Sill and Auxiliary structures, but did not bury them. Still, the amount of sediment transported was so large that the Corps was forced to perform a major dredging effort between July 2012 and March 2014 along the two structures’ inflow and outflow channels. This was the first such dredging operation since the two structures were built."