Rivergator Appendix XX
Low Water 2012
The seesaw from too much to too little water may be a sign of what’s to come as manmade global warming intensifies the water cycle, leading to more precipitation extremes, both heavy rains and drought events.
Historically, the winter lows for streamflow at St. Louis occur in late December through January, according to Steve Buan, a hydrologist with the National Weather Service in Chanhassen, Minn. According to NOAA data, January-November 2012 ranked as the third-driest such period on record for the Mississippi River basin north of Memphis, behind the Dust Bowl years of 1936 and 1934.
At the New Madrid Gage, in New Madrid, Mo., the Mississippi reached a record high of 48.35 feet on May 6, 2011. Just 15 months later, on Aug. 30, 2012, the gauge reading dropped to a record low of minus 5.32 feet. (River gauges are calibrated to a particular elevation, known as a “zero datum,” which means that they don’t always equal the depth of water in the channel. So in this case, the record low was 5.32 feet below the zero-datum elevation at New Madrid.)
In particular, the approximately 180-mile stretch of the Mississippi River between Cairo, Ill., and St. Louis is of the most concern for low-water levels, according to Victor Murphy, climate services program manager for the National Weather Service’s Southern Region in Dallas. The low water in the area is in stark contrast to 2011, when the Army Corps of Engineers was forced to blow up a levee near Cairo, flooding farmland, in order to save the town from devastating flooding.
One especially treacherous low-water section of the Mississippi is currently located near the town of Thebes, Illinois, where submerged rocks, known as “pinnacles,” jab toward the surface of the river, threatening to ground passing vessels.
On Monday, the Army Corps announced plans to release more water from Carlyle Lake in Illinois to aid in safe navigation along the Mississippi near Thebes, and the agency is also planning to blast submerged rocks and conduct dredging operations to keep barges and ships from running aground.
"Water from the lake will help provide the depth necessary for river commerce to pass Thebes, Illinois, where rock formations pose a risk to navigation at minus 5 feet and below on the St. Louis gage," the Corps said in a press release. The Corps said the water releases will provide an additional six inches of depth in this critical stretch of the river.
(From Climate Central)