The mouth of the Mississippi River is the staging ground for an epic wrestling match between saltwater from the Gulf of Mexico and freshwater from the river. Usually, the Mississippi’s powerful flow keeps the saltwater at bay. However, this year’s drought has weakened the river, allowing saltwater to intrude upstream. This intrusion has already contaminated drinking water in several towns in southeast Louisiana, and experts predict it could reach New Orleans by November. The ocean is currently winning the battle.
According to hydrologist Matthew Hiatt, this year’s saltwater intrusion is the result of various environmental events across the Great Plains, the Ohio Valley, and parts of the Mountain West. A combination of landside drought and rising sea levels is making saltwater intrusion during the dry season more frequent. This is not an isolated incident; it’s a trend that is likely to continue.
This is not the first time saltwater intrusion has occurred. During the Dust Bowl, New Orleans’ drinking water had salt concentrations 55 percent higher than current federal guidelines. In 1988, a wedge of saltwater came dangerously close to the water-intake plant for the eastern bank of Orleans Parish. In response to saltwater intrusion, the United States Army Corps of Engineers has built semi-temporary underwater dams, known as sills, four times in the past few decades. This year and 2022 mark the first consecutive times the Army has had to take such measures.
Human activity is also contributing to saltwater intrusion. Engineers have lowered the southernmost riverbed of the Mississippi over the years to accommodate shipping, providing more space for saltwater to infiltrate during low water levels. This, combined with sea-level rise and changing rainfall patterns, increases the likelihood of saltwater intrusion in the future.
The Mississippi River’s flow patterns are becoming more unpredictable and volatile. Rain in one region can offset drought in another, but when there is a shortage of water everywhere, the river’s levels drop. This type of saltwater intrusion is unique to the Mississippi River. Other estuaries, such as Mobile Bay Estuary, do not experience the same level of intrusion due to tidal fluctuations.
The Army Corps’ underwater dams work by stopping the saltwater flow on the river bottom. However, if the ocean’s water level continues to rise, these measures may become ineffective. As saltwater moves up the river, communities that rely on the Mississippi for drinking water must find alternative sources or invest in desalination systems. Saltwater intrusion can also have long-term effects on groundwater, leading to concerns about water quality beyond the river’s immediate vicinity.
Furthermore, saltwater intrusion can have significant repercussions for ecosystems, transportation, infrastructure, and public health. Saltwater can corrode pipes, contaminate water supplies with heavy metals, and disrupt shipping when sediment deposits clog the navigation channel. The southern part of the Mississippi is a delicate balance of interests, including shipping, farming, fishing, and tourism. Any major changes to the river’s dynamics could have far-reaching consequences.
While experts believe that the saltwater will likely recede by spring due to freshwater from the upper Midwest, the need for rain remains crucial. Rainfall is the only solution to the current saltwater intrusion problem. Without sufficient rainfall, the battles between saltwater and freshwater in the Mississippi River will continue, impacting ecosystems, communities, and infrastructure along the lower Mississippi.
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