Solutions for a salty future
One of David Zetland’s students who posts to his Blog The one-handed economist. Each year Prof. Zetland allows some of his students to write on various topics and he posts their words on his site. You can either comment here on AB or post to David Zealand’s site. The link is above. Pleease be polite.
“Solutions for a salty future”
Liliana writes* . . .
In September 2023, residents of New Orleans, Louisiana had salt water coming out of their taps (Sneath, 2023). The city declared a state of emergency as a “salt water wedge” moved up the Mississippi River from the Gulf of Mexico. Although the crisis was averted, the underlying issues remain for the city.
The source of the issue is clear: there is more room in the river and less fresh water to fill it. Much of the Mississippi lies below sea level in Louisiana, meaning that without enough fresh water flow, the river is vulnerable to salt water intrusion (NOLA). As yearly droughts increase in severity with global warming, the river’s flow is sometimes insufficient to stop the underflow of denser salt water (NOLA). Exacerbating this, the US Army Corps has dredged the Mississippi to increase cargo clearance for decades (Bliss and Hirji, 2023). Their most recent large-scale project in 2022, deepened parts of the river by 5 feet (1.5m), to 50 feet (15m) (Bliss and Hirji, 2023). These efforts have been touted as an economic success, allowing the Mississippi River Ship Channel to expand the already 450 million tons of exports that travel the route. However, with decreasing fresh water flow and rising sea levels as a result of climate change, these rewards are not worth the risks.
Salt water intrusion causes harm across every sector. For humans, high sodium concentrations can increase blood pressure (Chow, 2023). Salt water is much more corrosive than fresh water and could cause harmful chemicals to leach from pipes into drinking supply. Nearly all piping in New Orleans is made with lead, so corrosion could introduce serious public health risks, as was seen in Flint, Michigan (Chow, 2023). Salt can also corrode infrastructure, which could cost the city millions to replace. Finally, soil health and agricultural output would be at risk with farmers literally salting the earth (Chow, 2023).
Solutions vary. Current containment methods include constructing underwater sills (Bliss and Hirji, 2023). As salt water is much more dense than fresh water, the intrusion travels in the shape of a wedge along the base of the riverbed. Thus, what are essentially walls can be built along the riverbed to ensure that the wedge does not travel further upstream (see figure). Holes in the sills allow continued commerce along the river. Although effective short-term, this solution is unsustainable as it ignores the problem’s root causes and requires new sills each time the salt water wedge grows.
Other solutions include pumping water into the city, either from a pipeline constructed upstream or through a desalination plant (NOLA). Lastly, some propose new management of the city’s aquifers, currently drained annually during the rainy season as flood prevention. Instead, some suggest an increase in green spaces to mitigate the issue of floods and the use of the aquifer for drinking water (Sabo, 2023). This is a much more long-term solution but requires significant infrastructure changes. A combination of all the ideas mentioned above will likely constitute the city’s mitigation methods.
Bottom line: In New Orleans, the Mississippi River has far too much depth and not enough freshwater flow to fill it. As a result, salt water is infiltrating the city’s water supply, posing serious health and infrastructure risks. A variety of solutions including pumping water into the city and the construction of sills must manage these threats.
Solutions for a salty future – The one-handed economist