Saltwater Intrusion Study
A proposed longitudinal study of saltwater intrusion into the Greater New Orleans water supply and its effects on residents' health.
The 2023 low-water event.
In the fall of 2023, the Mississippi River's flow fell to about 150,000 cubic feet per second, against a safe threshold of roughly 300,000 cfs.1,2 With less freshwater pushing downstream, a saltwater wedge from the Gulf of Mexico moved upstream along the riverbed toward the drinking water intakes for the Greater New Orleans metropolitan area.
The U.S. Army Corps of Engineers built an emergency underwater sill (a barrier on the riverbed) to slow the saltwater, and water utilities issued advisories.2,1 The event raised hard questions about the long-term reliability of New Orleans's water supply if drought on the Mississippi becomes more common.
For weeks, salinity crept toward the intakes. Officials warned that the wedge threatened drinking water for close to a million residents across four parishes, including the Carrollton plant that serves New Orleans's east bank.1
A longitudinal health study.
The Saltwater Intrusion Study (SWIS) proposes following a population over time to measure how saltwater intrusion into a municipal water system affects health. Climate change is shifting river flows across the Mississippi basin, so these events are worth studying now.
The study would track salinity, chloride, and disinfection byproducts in treated water during and after intrusion events, and compare those measurements with health outcomes in the exposed population, including hypertension, kidney function, and other cardiovascular endpoints.
Research Questions
- •How do acute saltwater intrusion events affect treated water chemistry?
- •What are the cardiovascular and renal health impacts of elevated sodium in municipal water?
- •Do current water treatment processes adequately mitigate salinity during intrusion events?
- •What monitoring infrastructure is needed for early warning and adaptive response?
Saltwater wedge dynamics.
As river flow drops, denser saltwater from the Gulf of Mexico pushes upstream along the riverbed. Drag the slider to change the flow rate and watch the wedge move toward New Orleans.
Lower Mississippi, Head of Passes to New Orleans
Longitudinal profile: depth below the surface along the river. Denser Gulf water creeps upstream along the bed when the river runs low.
- Wedge toe
- ≈ RM 64
- At the sill, near Myrtle Grove
- Emergency sill · RM 64
- Holding: the toe is stopped at the sill
- Drinking-water intakes
- Pointe à la Hache RM 49 · Salty at intake
- 5 further upstream clear, incl. Carrollton
- Fresh river water
- Saltwater wedge
- Halocline (salt/fresh boundary)
- Channel bed & sill (schematic)
Illustrative model, not a forecast. Toe position is a straight-line fit from the Corps’ 300,000 cfs threshold to its projected worst-case 2023 toe (RM 103.7 at ~130,000 cfs); sill overtopping flows are calibrated to fall 2023. Bed profile is schematic. River miles and 2023 facts: USACE New Orleans District (DVIDS), Sept. 24, 2024; Corps intake table via FOX 8 WVUE, Oct. 5, 2023; NOAA U.S. Coast Pilot 5, ch. 8; Waterways Journal, Sept. 29, 2023; Christian Science Monitor, Oct. 23, 2023; NBC News, Sept. 26, 2023; WWNO, Sept. 19, 2023; National Park Service, Mississippi River facts.3,4,5,2,6,7,8,9
The case for a long-term study.
In 2023, officials said the saltwater wedge threatened drinking water for close to a million people in four parishes that draw from the Mississippi.1
The Army Corps has built emergency underwater sills near Myrtle Grove in 1988, 1999, 2012, 2022 and 2023, the last two years running.10
I found no long-term health study tracking the impacts of saltwater intrusion on a municipal water supply population. This proposal is designed to fill that gap.
Sources
- 1Why the saltwater wedge climbing up the Mississippi River is a wake-up call to the region · PBS News, Oct 10, 2023Close to a million residents in four parishes; river at 150,000 cfs, half of what is needed to keep salt water out; Plaquemines water advisories; Carrollton plant.
- 2Corps Augments Underwater Sill To Slow Salt Water Intrusion · The Waterways Journal, Sept 29, 2023Intrusion below 300,000 cfs; July sill; overtopped around Sept 20; raised to −30 ft from Sept 24 with a 620-ft notch; toe at RM 69.4 on Sept 27.
- 3USACE New Orleans District team receives 2024 Innovation Award for notched sill barrier used to arrest saltwater intrusion up Mississippi River · U.S. Army Corps of Engineers, New Orleans District (DVIDS), Sept 24, 2024Belle Chasse RM 75.5, Carrollton RM 104.7; sill −55 → −30 ft; 2023 toe RM 69.4 (surface RM 54.4); projected RM 103.7 (surface RM 88.7) with the original sill.
- 4Significant adjustment in saltwater wedge timeline delays some impacts by nearly a month, if at all · FOX 8 WVUE, Oct 5, 2023Corps intake river miles: Belle Chasse, Dalcour, St. Bernard, Algiers, Carrollton.
- 5United States Coast Pilot 5, Chapter 8: Mississippi River · NOAA Office of Coast SurveyRiver miles above Head of Passes and channel depths.
- 6Saltwater influx tests communities near Mississippi's mouth · The Christian Science Monitor, Oct 23, 2023Corps: 300,000 cfs is "the magic number"; the RM 64 sill raised the bed nearly 35 ft.
- 7New Orleans braces for drinking water emergency from drought-stricken Mississippi River · NBC News, Sept 26, 2023Flow of 148,000 cfs the week the wedge overtopped the sill.
- 8Salt water threatens South Louisiana drinking water second year in a row amid severe drought · WWNO, Sept 19, 2023Flow forecast to drop to 130,000 cfs by mid-October; 1988 record low of 120,000 cfs let the wedge reach Kenner.
- 9Mississippi River Facts · National Park ServiceAverage flow at New Orleans: 600,000 cfs.
- 10USACE to construct underwater sill to arrest saltwater progression into Mississippi River · Governor’s Office of Homeland Security and Emergency Preparedness (USACE release), Aug 29, 2024Sills at River Mile 64 near Myrtle Grove in 1988, 1999, 2012, 2022 and 2023.