What Six Years Of New Corps Data Tell Us About The Rivers

In March 2019, with the Mississippi River above flood stage at Baton Rouge for what would become 211 consecutive days, Bill Frederick — liaison between the U.S. Army Corps of Engineers’ Mississippi Valley Division (USACE-MVD) and the National Weather Service — published “Precipitation Trends in the Mississippi River Watershed,” documenting a century of rising basin rainfall and telling readers, in effect, to expect more high-river events.

Six years later, in March 2025, USACE-MVD published an update: Anna Wolverton’s “Greater Mississippi River Basin Precipitation Trends” — same watershed, more stations, more seasons, seven more years of record. Those years held the largest flood by volume in the river’s documented history (2019) and the start of a drought sequence that has required emergency saltwater sill construction on the Mississippi River Ship Channel (MRSC) every year since 2022. The potential need for the wedge is being closely monitored now as low-water conditions continue, and the saltwater barrier’s construction could be required in 2026.

Read side by side, and against USACE-MVD’s January 2026 “State of the River” and “Summary of 2022–2025 Low Water Events,” the two reports produce a picture neither delivers alone. The central finding:

The Mississippi River Basin is not behaving in a way it has never behaved before. It is behaving harsher, higher, lower and faster, with less time at average flows.

A Word That Has Stopped Working

“Unprecedented” now appears in nearly every account of a Mississippi River extreme, worn smooth by use. The record is more careful: saltwater advanced farther inland in the 1950s than in any recent event, and the Baton Rouge record low, 0.1 feet, dates to 1894. Comparable dry-period clustering occurred in the 1950s, before saltwater sills existed. The practice dates to 1985 and the Ship Channel Deepening Project (40 to 45 feet). The absence of a 1950s emergency record reflects the absence of the practice, not of the drought.

What is without parallel is narrower: the frequency and clustering of extremes in the operational record — five Bonnet Carré operations in five years, then four consecutive years of emergency saltwater sills. But the finding that should change how planning gets done has nothing to do with records.

The Cycle Is Real. So Is The Trend.

USACE-MVD’s position, stated in January 2026, is that recent low water is “directly related to below average seasonal rainfall” and reflects the basin’s natural oscillation between wet and dry phases, driven largely by El Niño and La Niña. These droughts, the division is emphatic, are not unheard of. Wolverton’s data sounds different but is not contradictory: within that oscillation, the amplitude is growing.

The cycle explains why there is a dry period right now. The trend explains why dry periods now produce emergency responses that used to be rare, and why wet periods produce floods that break century-old records.

Basin-average annual precipitation has risen about 0.51 inches per decade since 1950; over 1994–2023 that climbs to 0.6, accelerating, not merely continuing. In the Ohio River Basin, the acceleration is stark: 0.81 inches per decade from 1950 to 1993, then 1.52 from 1994 to 2023 — nearly double.

That matters more than any other sub-basin number: roughly 90 percent of the water in the Ship Channel at New Orleans (Mile 95 Above Head of Passes, or AHP) is already in the river by the time it passes Cairo, Illinois, and the Ohio and Tennessee basins supply about 60 percent of Lower Mississippi flow. When the Ohio’s precipitation trend doubles, that is the Ship Channel’s water supply changing character.

The Extremes Are Getting More Extreme At Both Ends

Because Frederick and Wolverton measure the same things with different amounts of data, the direction of change is visible. Both cite the National Climate Assessment, the federal government’s periodic climate report. Frederick, using the third edition (NCA3), reported a 37 percent increase in precipitation falling during the heaviest 1 percent of daily events across the Midwest from 1958 to 2012; Wolverton, using the fifth (NCA5), reported 45 percent for 1958–2021 — the same metric, eight percent higher, nine years later.

At Cairo, both reports reach the same conclusion: minor flood frequency has been near saturation for a century, moderate flood frequency flat since the reservoirs came online, but major flood frequency roughly doubled — from 13 to 20 percent of years in the early record to 30 to 38 percent in the most recent windows. The reservoirs are doing what they were built to do; the events that exceed their capacity are arriving twice as often.

At Baton Rouge, one of the critical Ship Channel gages for deep-draft commerce on the MRSC, major flood frequency went from 3.3 percent of years in 1955 to 1984 to 33.3 percent in 1995 to 2024, a tenfold increase; minor flood frequency has nearly tripled, to 70 percent of years.

And the other end. Frederick’s low-water data, ending in 2017, told a story of improvement: upstream reservoirs completed in the 1940s to 1960s raised minimum stages at Cairo from roughly 7.5 to 8.5 feet to 11.5 to 12 feet. Wolverton’s data, ending in 2024, shows that improvement interrupted — years with Cairo below 10 feet rose from 30 percent to 43 percent. The reservoirs have not stopped working; without them, 2022 to 2025 stages would have fallen considerably lower. What changed is the weather. The 1950s drought was a sustained multi-year deficit; the 2022 to 2025 events came against a wetter annual baseline, punctuated by intense, high-temperature crashes — flash droughts.

One Mechanism, Both Extremes

A single physical process produces both outcomes, which is why treating flood and drought as separate problems has become untenable. Rising temperatures increase evapotranspiration (ET), the moisture lost from soils and plants. Higher ET dries soils faster between rain events even in years when rainfall is up — the drought half — and puts that moisture into the atmosphere, where it can fall as intense precipitation — the flood half.

In Wolverton’s framing, the basin spends less time in near-normal conditions and more at one extreme or the other. Projections agree — more days above the 90th percentile of precipitation, more days with none, fewer in the ordinary middle.

Streamflow, meanwhile, has risen far out of proportion to precipitation. Precipitation is up 10 to 25 percent since 1900; streamflow is up 25 to more than 100 percent, with land use change — tile drainage, urbanization, reduced infiltration — accounting for much of the gap. Pilots have reported the practical version for 15 years: more current at the same river stage.

What It Costs

Between 2016 and 2020, the Bonnet Carré Spillway was operated five times in five years: 2018 and 2019 back-to-back, the first consecutive-year operations in its history; twice in 2019 alone, the only double-opening ever, with the second running 79 days, the longest on record. It was operated 10 times total between 1937 and 2011.

Then, beginning in 2022, there were four consecutive years of emergency saltwater sill construction. In 2023, saltwater advanced to Mile 69.4 AHP, the farthest in the modern record; the sill had to be raised, with a navigation notch built into it so one-way deep-draft traffic could pass — an engineering first — and a federal emergency was declared. In early 2025, a spike in river levels almost required the Bonnet Carré, and by fall the sill was required at a flow of only 175,000 cfs: both emergency responses nearly in one calendar year. Unprecedented extreme water levels could see both the operation of Bonnet Carré and the construction of the saltwater sill in the same year, unimaginable a decade ago.

Flood and drought damage navigation through different channels. Floods hit the deep-draft Ship Channel through Southwest Pass shoaling: in 2019, seven dredges worked simultaneously, draft restrictions persisted 205 days, and the Corps of Engineers put cargo impacts at $6 to 7 billion. Droughts force 25 to 40 percent load reductions on shallow-draft navigation and drive saltwater intrusion; the 2022 drought was estimated at roughly $20 billion across the inland system, with barge spot rates at St. Louis hitting an all-time high of $105.85 per ton.

Easy to miss: the deep-draft Ship Channel has seen almost no draft restrictions during the recent droughts. The only ones since the 2022 deepening are linked to pipeline issues, not shoaling — partly channel depth, partly Corps responsiveness, including early and regional hopper dredge contracts awarded after the extreme 2019 event with Coalition input accepted.

Two Things Worth Watching

It’s worth watching a compounding factor emergency concern of the navigation industry that also impacts drinking water that is not yet understood outside the industry. Three uncontrolled crevasses on the east bank below New Orleans — Mardi Gras Pass (Mile 43.7 AHP), Neptune Pass (Mile 24 to Mile 22 AHP) and Fort St. Philip (Mile 20 to Mile 18 AHP) — hemorrhage stream power out of the river, weakening the hydraulic head that holds the saltwater wedge back and also allowing the inward flow of saltwater from the Mississippi Sound. The three crevasses have been documented flowing inward during low water, injecting saline water higher into the system than the traditional passes do. Tulane Coastal Science modeling indicates that closing them would substantially reduce the need for annual sills; the Corps of Engineers has placed hundreds of thousands of tons of rock at Neptune Pass to reduce the outward flow.

The second thing worth mentioning is new in 2026: flocculation (see the July 17 Tributaries Volume 2) was reported by pilots above Head of Passes for the first time, as far upriver as Mile 9, previously recorded only in Southwest Pass. The Coalition attributes the migration to the loss of stream power through the crevasses below Venice — the Corps estimates 30 to 51 percent of the river’s stream power — and to repeated low stages. Work with Tulane’s Department of River-Coastal Science and Engineering is underway.

The Planning Implication

More abnormal, less normal. The record books are the wrong place to look for what has changed here. The change is in the middle — the ordinary years the system was designed around — and they are getting harder to count on.

The full synthesis, “Mississippi River Basin Hydroclimate Synthesis,” by Dennis Lambert, P.E., F.ASCE, Bowman Consulting, and Sean M. Duffy, Sr., Big River Coalition, LLC, synthesizes Frederick (2019) and Wolverton (2025), USACE Mississippi Valley Division, with the Division’s January 2026 “State of the River” and “Summary of 2022–2025 Low Water Events.”