Given news about saltwater incursions along the lower Mississippi River, we asked our colleague Gen. (Ret) Thomas Sands for his thoughts. Tom was president of the Mississippi River Commission and commanded the Army Corps of Engineers Lower Mississippi River Division. What follows are his insights:
Saltwater from the Gulf of Mexico is moving up the Mississippi River and may seep into New Orleans’ water intake pipes, threatening drinking water for the city’s residents. President Biden has declared a federal emergency to combat this issue and officials are taking several steps to avoid scenarios that could threaten lives and harm the region’s economy.
During the 1988 drought, I commanded the Corps of Engineers division in this region and witnessed firsthand the impacts of saltwater intrusion during unusually low flow conditions.
To be clear, saltwater intrusion is not a new problem. But what is new, and what should concern all Americans, is that saltwater intrusions are happening more frequently. If the climatic conditions driving this problem become the norm in this area or if intrusions happen with significantly greater frequency, New Orleans may be in trouble.
To appreciate the breadth of this challenge, first look at the region’s geography. The countervailing pressures from the Gulf of Mexico saltwater and fresh water coming down the Mississippi River are in a constant battle. During periods of low rainfall, or when the river’s current is weaker, saltwater will steadily advance toward New Orleans. To fight against the advance, the U.S. Army Corps of Engineers must act quickly and decisively. To slow the current saltwater intrusion, the Corps is adding to a sill on the river bottom below New Orleans. This sill raises the river bottom by about 25 feet and the Corps projects this will slow the saltwater “wedge” by about 2 weeks.
For decades, the Corps had to construct a new sill about every 10 years. It constructed one in 1988 in response to drought across the Midwest. The Corps constructed another sill in 1999 because of low rainfall in the Ohio River basin and again in 2012.
But the Corps has now had two consecutive years of new sill construction due to record low water levels on the Mississippi.
Living with water is second nature for the people who survived Katrina and saltwater intrusion has always been associated with low water flows in the Mississippi River. However, rarely has the intrusion significantly impacted public water supply facilities the way it has this year. Unchecked, saltwater will impact the major intake structures for New Orleans as well as the adjoining Jefferson Parish.
New Orleans should be able to navigate the current water quality issues, but it will take a thoughtful effort to identify the reasonable expectations associated with determining the impact of changing climatic conditions and seal level rise on saltwater intrusion in the future.
This impact appears to be growing. During the 1988 drought the salt water wedge did not reach upriver past New Orleans major municipal water intake facilities. But the problem facing officials today is that Mississippi River basin rainfall predictions indicate flow conditions may not improve until January.
This is why officials had to take action to ensure safe drinking water. For small volume water facilities, a combination of delivering fresh water via barge and use of reverse osmosis machines are two solutions. The Corps is projected to barge 36 million gallons of fresh water daily.
But for larger volume facilities, options are more complicated. Responsible officials have decided to construct a fresh water piping system from upriver to water intake facilities in Jefferson Parish and New Orleans.
Jefferson Parish has a facility on each side of the river with flexible piping sufficient to carry the fresh water volume needed from the “Kenner hump,” an area upriver from the treatment facilities where the river bottom’s change in grade limits progression of a saltwater wedge. The Jefferson pipeline will be approximately 10 miles and leaders are comfortable the project will be completed prior to the projected arrival of the saltwater.
New Orleans is planning to install high-density polyethylene piping, approximately 15 miles in length, for the facility at “Carrollton” on the east bank to support the 130-150 million gallons per day demand. The cost estimate for the New Orleans solution is in the $250 million range. October 28th is the date saltwater is expected to impact the New Orleans facility. Options are being developed to provide “gap” support should the project not be completed by the 28th.
The bigger question relates to whether saltwater intrusions near New Orleans become more common. Anticipated sea level rise is likely to increase incursions in both the river system and aquifers. In sum, the region must look for permanent fixes to ensure it can meet future demand for safe water. This will take thoughtful effort to identify reasonable expectations associated with determining the impact of changing climatic conditions and sea level rise on saltwater intrusion.
Gen. (Ret) Tom Sands commanded the Army Corps of Engineers New Orleans District and Lower Mississippi Valley Division.