The Mississippi River is experiencing historical levels of drought for the second year in a row, with water levels at a record low of 3.5 metres below average at Memphis on the 10th of October. According to the U.S. Drought Monitor, more than 98% of the Mississippi River Basin experienced some level of drought conditions during September and October. In October, 2% of the basin was experiencing moderate drought, 20.9% of the basin was experiencing severe drought, 43% of the basin was experiencing extreme drought and 34.2% is experiencing exceptional drought. This year, it is these drought conditions that are largely responsible for the upstream movement of salt water. However, human influences such as dams, levees and dredging have altered the natural flow of the river, and the gulf is also experiencing sea level rise due to climate change.
By the 12th of October, the saltwater wedge had moved upriver by a full ten kilometres. As the flow of the river decreases, the pressure of freshwater flowing into the ocean at the river’s mouth is decreasing, and a wedge of saltwater is slowly creeping up the river. The result is saltwater intrusion into coastal freshwater sources. Louisiana’s water supplies are affected by the increasing salt levels in the water, prompting emergency transports of freshwater by barge to water treatment and pumping stations by the U.S. Army Corps of Engineers which are expected to continue into January next year. There have been fears that the upstream movement of saltwater could begin to affect the water supplies of New Orleans also, but according to the U.S. Army Corps of Engineers, the river flows did recover to an extent that would protect the intakes around New Orleans from the upstream movement of salt.
The drought has led to transport restrictions for barge companies which usually transport crops downriver from the Midwest to the Gulf of Mexico. Barges have been induced to reduce their loads as the depth of the river has dropped, limiting traffic options. The Mississippi River transports over 450 million tonnes of goods annually. However, American wheat shipments for instance, of which two thirds are shipped to the Gulf of Mexico along the Mississippi have dropped to record low levels as a result of the drought.
The Mississippi River basin is the largest in the United States: it rises in Lake Itasca in Minnesota and flows in a southerly direction for 3,766 km, draining 59% of the rivers of the country.