Excerpt
The usually abundant slow soaking rain systems and evening thunderstorms that characterize the Great Plains climate from May through August (Hoerling 2013) were absent in 2012. As a result, the Ohio and Mississippi rivers dropped to near record levels from July of 2012 through January of 2013, and the US Army Corps of Engineers (USACE) faced a new challenge to their ability to control the Mississippi River. The 2012 drought reduced the channel depths on the upper Mississippi River between Cairo, Illinois, and St. Louis, Missouri, to only 0.3 to 1.8 m (1 to 6 ft) above the 2.7 m (9 ft) deep navigation shipping channel created by USACE in response to the 1930 Rivers and Harbors Act. Of greatest concern was the bedrock-lined river shipping channel near Thebes, Illinois, which threatened to ground barge traffic transporting critical agricultural supplies, including fertilizers and grain.
Although the USACE systematically surveys the river bottom and routinely dredges sand accumulation within the Mississippi River to maintain the shipping channel, the Thebes section of the river posed a more difficult engineering situation. Ice Age glaciers and more recent seismic activity created the “Thebes gap” in the upland bedrock ridge and rerouted the ancient Mississippi…
- © 2014 by the Soil and Water Conservation Society
