Freeboard

River-Side

Freeboard is the distance between the surface of the water and the top of the wall that is holding it. On the Mississippi River levee south of Donaldsonville, Louisiana, in Assumption Parish, on a Tuesday in October when the river stage at the Donaldsonville gauge reads 14.7 feet, the freeboard is approximately nine feet. Nine feet of compacted earth and clay between the brown surface of the river and the place where the levee ends and the air begins. Nine feet is the distance across a small bedroom, the height of a ceiling in a house built before the Second World War. Many of the houses behind this levee were built before the Second World War.

In the spring of 2024, during a flood that crested at 23.1 feet at the Donaldsonville gauge, the freeboard was eleven inches. Volunteers and inmates from the parish jail were stacking sandbags along the crest at two in the morning, working under floodlights, layering the bags in a herringbone pattern that the Army Corps of Engineers had diagrammed in a field manual none of them had seen. They were adding to the levee the way the levee had always been added to — by hand, in crisis, in the dark.

The Mississippi River levee system extends approximately 3,500 miles along both banks, from Cape Girardeau, Missouri, to the Head of Passes below Venice, Louisiana. Include the tributary levees — the Arkansas, the Red, the Yazoo, the Atchafalaya — and the total exceeds 12,000 miles. Most of it was built between 1882 and 1968, designed to withstand a flood roughly equivalent to 1927, when the river broke through in 145 places and inundated 27,000 square miles.

The 1927 design standard was called the “project flood” — the worst possible combination of simultaneous tributary floods, peak rainfall, maximum snowmelt. Every levee was engineered to contain it with three feet of freeboard. The height of a kitchen counter.

There are several things wrong with this design, and they compound.

First: the project flood was a statistical artifact. It was derived from roughly 150 years of observations, some unreliable. The Mississippi Basin has been producing floods for 10,000 years. Basing the design flood on 150 years of data is like basing the speed limit on the fastest car you’ve personally seen.

Second: the levees have changed the river. A natural flood spreads laterally — the velocity drops, sediment settles, the floodplain absorbs it over weeks. Levees confine the water to the channel. It rises vertically instead of horizontally. A flood that would have been twelve feet deep and three miles wide becomes twenty-four feet deep and a quarter mile wide.

Third, and this is the one that keeps hydraulic engineers awake: the channel is rising. The Mississippi carries 500 million tons of sediment per year — the Rockies, the Great Plains, the farms of Iowa. In a natural system, that sediment deposits on the floodplain during floods. In the leveed system, it drops in the channel. The bed rises. The flood stages rise with it. The levees must be raised to match. At the Old River Control Structure, flood stages have risen roughly twelve feet since the levees were built. The height of a room.

The arithmetic is not difficult. Three feet of freeboard above a flood calculated from limited data, on a river whose flood stages are rising because the levees themselves have altered the hydraulics. Every decade of successful flood control narrows the margin.

I drove the levee road south from Donaldsonville on a morning when the river was low — eleven feet at the gauge, thirteen feet of freeboard — and the whole structure looked absurdly overbuilt. The levee at this point is twenty-four feet above the surrounding grade, wider at its base than a four-lane highway, with a twenty-foot paved crown and side slopes of one vertical to three horizontal, planted in Bermuda grass. From the crown, the river is a brown plate, calm, deceptively slow. Barges go by in silence. The far bank is a mile away and furred with willows.

The levee is composed of compacted clay, sourced from borrow pits dug parallel to the levee alignment. The clay is placed in twelve-inch lifts, each lift compacted to 95 percent of standard Proctor density, a measure of soil compaction named for Ralph Proctor, a field engineer with the Bureau of Reclamation who published his compaction test in 1933. The clay must meet specific plasticity requirements — too sandy and it erodes, too plastic and it cracks. The ideal levee clay is a silty clay of medium plasticity, classified as CL in the Unified Soil Classification System, with a liquid limit between 30 and 50 and a plasticity index between 10 and 25.

A levee that fails because it was poorly built is a construction failure. A levee that fails despite being built to specification is a design failure. And a levee built precisely to specification, inspected annually, that is overtopped because the river has exceeded the conditions the specification was written for — that is something else entirely.

Land-Side

I turned around on the levee crown and looked the other direction. On the river side, there was the river, the batture, and beyond that, nothing human. On the land side, there were houses.

They were close. Some within a hundred yards of the levee toe. Small houses — vinyl siding, metal roofs, elevated foundations not elevated enough. Yards with plastic furniture and truck tires and children’s bicycles left on their sides in the grass. At the end of one driveway, a hand-lettered sign for boiled crawfish, with a phone number. In front of another, three white crosses with plastic flowers.

Assumption Parish: 22,000 people, down from 25,000 at the 2000 census. Median household income $42,000. Poverty rate 22 percent. The population is 33 percent Black, concentrated in the unincorporated communities along the river — Plattenville, Bayou L’Ourse, Superville, Belle Rose. If you drive the River Road on the levee crown, you see the river on your left and, on your right, below you, a landscape that recedes, as though the levee were the rim of a bowl and the houses at the bottom.

That optical effect is not only optical. The land is sinking.

Subsidence in Assumption Parish runs between eight and twelve millimeters annually — half an inch per year, five inches per decade, two feet per century, if the rate held steady. It won’t. The causes compound: compaction of alluvial sediments under their own weight, withdrawal of groundwater and hydrocarbons, tectonic adjustment to the absence of the glaciers that once depressed the northern continent and whose removal is still causing the southern half to sink. The levee itself contributes — its weight compresses the soil beneath it, lowering the surrounding land relative to the crest, so the levee appears to grow taller while the ground drops away.

In 2012, a sinkhole opened in Bayou Corne, ten miles north of Donaldsonville, when a salt dome cavern operated by Texas Brine Company collapsed. It began as a crack in the earth, then a depression, then a hole filled with brine and liquid hydrocarbons. Trees tilted and fell into it. The bayou bubbled with methane. Three hundred and fifty residents were evacuated and never returned. Texas Brine paid settlements. The state issued orders. The sinkhole is still growing. Last measured at thirty-seven acres.

The sinkhole shares a geology and a logic with the levee system. The same extraction economy that created the need for levees — cotton, sugar, petrochemicals, all requiring dry land in a wet landscape — hollowed out the substrate. The land is sinking because the weight on top of it was increased and the material beneath it was removed. The people living inside this process did not choose it. The ones who understand it cannot afford to leave.

I spoke with a woman in Plattenville who had lived behind the levee for forty years. Her name was Odette. She was seventy-one. She sat on her porch in a lawn chair, and she could see the levee from where she sat — the grass slope rising above the roofline of her neighbor’s house, a green wall against the sky. She told me she had never been on top of it.

“I don’t go up there,” she said. “What for? To see the water?”

She told me about the flood of 2016 — not the river flood, the rain flood. In August 2016, a low-pressure system stalled over southern Louisiana and dropped more than two feet of rain in three days. The river rose, but the levees held. The flooding came from behind — from the interior, from the drainage canals that couldn’t handle the volume, from the bayous that backed up because their outlets to the river were blocked by floodgates closed to prevent the river from coming in. The system designed to keep the river out also kept the rain in. Odette’s house took three feet of water.

“The pump stations couldn’t keep up,” she said. “They only have so much capacity. And the water had nowhere to go because they close those gates when the river is high. So the river is high on one side of the levee and the rain is rising on this side and we’re in between.”

The levee holds back the Mississippi. It does not hold back the rain, the subsidence, the saltwater intrusion, the insurance cancellations, the slow economic death of a parish that has been losing population for twenty-five years.

River-Side

At the Old River Control Structure, 65 miles upriver from Donaldsonville, the Corps maintains what may be the most consequential piece of infrastructure in the United States. The complex — three structures built between 1963 and 1990 — regulates the distribution of flow between the Mississippi and the Atchafalaya. Without it, the Mississippi would have abandoned its present channel sometime in the late twentieth century, diverting down the shorter, steeper Atchafalaya route to the Gulf. New Orleans, Baton Rouge, and every city between them would be left on a tidal bayou. The petrochemical corridor — Cancer Alley — would lose its cooling water, its process water, its transportation corridor.

The structures limit the Atchafalaya to 30 percent of the combined flow — a number established by Congress in 1954. It is not a hydrological number. It is a political number. The river does not recognize the compromise. Every flood season, the pressure differential across the structure increases, and the Corps opens gates and monitors the vibrations in the concrete and writes reports that assess the probability of failure using language calibrated to avoid the word “imminent.”

In April 1973, the low sill structure — the original 1963 facility — suffered catastrophic partial failure. The flood scoured the foundation, undermining the concrete apron. Seven of eleven bays showed significant structural damage. The engineers found it had come within inches of complete collapse — immediate, irreversible capture of the Mississippi by the Atchafalaya. In their reports, they called it “near failure.” A second auxiliary structure was built in 1986 to share the load.

But the river is still going west. The gradient advantage of the Atchafalaya increases with every foot of sediment that aggrades in the Mississippi’s channel. The structures are holding. For now. Everything downstream of Old River — every refinery, every port, every neighborhood, every house behind every levee — exists in the “for now.” The temporal frame of human habitation in southern Louisiana is maintenance time — the interval between inspections, between repairs, between the last crisis and the next one.

At the Donaldsonville levee, inspections happen twice a year — before and after flood season. Visual survey of the slopes, the crown, the toe drains, supplemented by readings from piezometers embedded in the levee body that measure pore water pressure. Elevated pore pressure indicates seepage, which indicates piping — the internal erosion of soil particles that can hollow a levee from within. Piping is worse than overtopping. The water doesn’t come over the wall. The wall comes apart.

The inspection reports are public documents, and I read several years’ worth. They are written in the language of routine — “no significant distress noted,” “vegetation control adequate,” “animal burrows repaired.” The word “adequate” appears frequently. A doctor’s chart that says “stable” on every visit but never says “healthy.”

Land-Side

There is a church in Belle Rose, on the land side of the levee, called Greater Zion Baptist. It was built in 1947 on a concrete slab foundation, and the slab has cracked in several places, and the cracks have been filled with epoxy, and the epoxy has cracked, and the building lists slightly to the south, toward the lower ground, toward the direction in which the entire parish is slowly tilting. The congregation is smaller than it was. The young people leave. They go to Baton Rouge, to Houston, to Atlanta, to places where the ground does not betray the architecture.

The ones who stay are not staying out of ignorance. Odette knew her house was sinking. She knew the levee was not a guarantee. She knew about the sinkhole in Bayou Corne and knew the salt domes under her own property were not fundamentally different from the one that collapsed. She knew about the FEMA buyout — $68,000 for a house she’d lived in for four decades, in a market where $68,000 would purchase, in Baton Rouge, a down payment and a commute and the loss of everything she recognized as her life.

She stayed because she understood the risk and also understood what the buyout programs, the relocation assistance, the elevation grants did not account for. The cost of leaving is the garden you have tended for thirty years, the church where you were baptized, the cemetery where your mother is buried in ground that will, eventually, be underwater. It is the neighborhood where someone checks on you when you’re sick and brings food when you’re grieving and knows your name and your mother’s name and the name of the man who built your porch.

The people who design relocation programs count units. They calculate square footage. They measure the distance from the new site to the nearest grocery store and call it “access.” They do not measure the distance from the new site to the cemetery, or the particular bend in the bayou where your grandfather taught you to fish.

Assumption Parish has lost 3,000 people since 2000. Not to a single catastrophe. To the jobs that left when the sugar mills closed, the insurance canceled when the flood maps were redrawn, the schools consolidated when enrollment dropped, the roads that washed out and took longer each time to repair. The levee holds. The parish empties anyway.

River-Side

In the geological record, the Mississippi has changed course roughly every thousand years. The process is called avulsion — the river builds its channel higher with sediment, perches above the surrounding floodplain, and eventually a flood breaches the bank and the water finds a shorter path to the Gulf.

Southern Louisiana is a palimpsest of abandoned channels — Bayou Lafourche, Bayou Teche, the Atchafalaya itself — each one a former course of the Mississippi, marked by a ridge of slightly higher ground flanked by backswamp. The current channel, running from Baton Rouge to New Orleans to the birdfoot delta, has been occupied for roughly 600 years. The Atchafalaya, 150 miles west, offers a route to the Gulf that is half the distance and three times the gradient. The Corps has been stopping the river from taking it for sixty years. Sixty years against a geological process that has been operating for 7,000.

I stood on the levee south of Donaldsonville and tried to hold two timescales at once. The river’s — millennia, avulsions, sediment drifting toward the Gulf. In that frame, the levee was a momentary scab. The river would shed it with a shudder and a redirection and an indifference so total it was not even contempt.

The human timescale was different. In that frame, the levee was the reason Donaldsonville existed, the reason 2 million people lived in New Orleans, the reason the port system handled 500 million tons of cargo per year. Remove the levee and you remove the premise of settlement. You return southern Louisiana to the river, and the river returns it to the swamp, and the swamp returns it to the Gulf, and the Gulf accepts it without comment.

You cannot make the river permanent. You can only maintain the infrastructure that creates the impression of permanence, and you can maintain it for a while — a century, maybe two — before the maintenance becomes untenable, or the river exceeds the design, or the money runs out, or the climate shifts the rainfall patterns in ways the original engineers could not have modeled.

Risk, in the engineering sense, is a probability multiplied by a consequence. The Corps estimates the probability of levee failure at Donaldsonville at less than 1 percent in any given year. The consequence is property damage, displacement, potential loss of life. The product is a number that can be ranked, budgeted against.

What the calculation excludes is who bears it. A family in a $400,000 house on higher ground with flood insurance and relatives in Baton Rouge faces a consequence that is categorically different from a family in a $68,000 house on subsiding ground without insurance, without a car, without anywhere to go. The same flood, the same levee failure — and the outcomes are as different as the lives were before the water arrived.

Land-Side

The first levees in Louisiana were built by enslaved Africans under French colonial rule. The Code Noir of 1724 required slaveholders to construct and maintain levees along the river frontage of their plantations. The labor was digging clay by hand, hauling it in baskets, compacting it with wooden tampers — performed by people who were the property of the people the levee protected.

After the Civil War, the labor shifted to convict leasing. Black men, arrested under vagrancy laws designed to criminalize being free and unemployed, were leased to levee contractors. The death rates were appalling. The levee boards knew. The arrangement continued because the levees had to be built and the labor had to be cheap and the people who benefited were not the people who died building them.

The extraction did not end with convict leasing. It continued through the twentieth century in the form of land-use decisions — where the refineries went, where the waste ponds went, where the levees were highest and where they were lowest, where the pump stations were maintained and where they were allowed to degrade. Cancer Alley — the 85-mile stretch of petrochemical plants between Baton Rouge and New Orleans — sits behind levees, on land cleared and drained and protected by the labor of enslaved people. The communities downwind of those plants are, overwhelmingly, the descendants of the people who cleared it.

Without the levee, no plantation. Without the plantation, no refinery. Without the refinery, no community meetings in church basements where people hold up photographs of their dead and ask the representatives of multinational corporations to explain the particular cruelty of being poisoned by an industry that exists because your ancestors were forced to make the ground it stands on habitable.

The levee is dirt. Clay, silt, compacted to 95 percent Proctor density, planted in Bermuda grass, inspected twice a year. In Louisiana, the decisions about what the dirt makes possible have been consistent for three hundred years.

River-Side

During the flood of 2011, the Morganza Floodway was opened for only the second time since 1954. A major general authorized the opening after determining the flood would otherwise overtop the levees protecting Baton Rouge and New Orleans. Twenty-five thousand people lived in the floodway’s inundation zone. They were evacuated. Their property was flooded. Their sacrifice — the Corps uses the word “sacrifice” in its technical documents, without apparent discomfort — protected the cities downstream.

The sacrifice areas are built into the system. The Morganza, the Bonnet Carré, the Birds Point-New Madrid Floodway in Missouri — places where flooding is planned, where the land is designated for inundation so that other land can remain dry. The people who live in them know, mostly. They receive compensation, sometimes. They return and rebuild, usually.

But a sacrifice requires consent. The family in the Morganza Floodway did not design the system that designates their home as expendable. They were placed there by the same accumulation of economic and racial history that placed Odette behind the levee in Plattenville — restricted housing, limited employment, land that was available because it was risky and therefore cheap. The sacrifice is extracted, as the labor was extracted, as the wealth of the Mississippi Valley was extracted from the people who worked it and deposited, like alluvial silt, in the portfolios of people who never see the river except from an airplane.

Land-Side

I went back to Odette’s porch in the afternoon. She had made coffee — dark roast, chicory-laced — and poured it into mismatched cups and set them on the railing.

“My grandmother was born in this parish,” she said. “My great-grandmother. My people have been here since before the Civil War. Since during. You understand? We didn’t come here. We were brought here. And then we stayed because it was the only here we had.”

She looked at the levee — a ridge of green against the sky, two hundred yards away, high enough to block the view of the river. She had never been able to see the water from her house.

“They came around after 2016,” she said. “FEMA people. Clipboard people. Told me I was in a flood zone, which I already knew, because I was standing in a flood. Told me I could apply for a buyout. I asked how much. They said they’d assess the property. It took eight months. Eight months to tell me my house was worth sixty-eight thousand dollars. I said, sixty-eight thousand? I’ve put more than that into this house in thirty years. They said that’s the fair market value. I said, fair to who?”

Fair to who. The levee is a hydraulic instrument. It manages water. It does not measure the differential impact of its failure on populations separated by income, by race, by the accumulated weight of three centuries of decisions made by people who will never stand on Odette’s porch.

The people who set the levee’s height and determine its alignment and decide which sections are reinforced and which are deferred — they know that the people behind this section are poorer and Blacker and older than the people behind the levees protecting the petrochemical plants upriver. They know that when the freeboard narrows to eleven inches and the sandbags go up at two in the morning, the people filling the sandbags are not the people who profit from the land the sandbags protect.

The levee holds. Another year passes. The reports say “adequate.” The river rises a fraction of an inch in its channel. The land sinks a fraction of an inch behind the wall.

River-Side

The Mississippi will take the Atchafalaya. Not this year. But the gradient advantage increases every year, and the structures age, and the floods test them, and one day a flood will come that was always possible and the design chose not to accommodate, and the structures will fail, and the river will go west.

When that happens, the levee south of Donaldsonville will become irrelevant — not because it fails but because the river inside it will diminish. The flow will drop. The channel will silt in. The water will turn brackish as the Gulf tide pushes upriver. The refineries will close. The port will close.

And the people behind the levee, in Plattenville and Belle Rose and Bayou L’Ourse, will still be there. On sinking ground, in a parish without a tax base, behind a wall that protects them from nothing, in houses their grandmothers built in a country that promised the ground would hold.

Land-Side

I asked Odette what she thought would happen.

“Same thing that always happens,” she said. “The water comes, or it doesn’t. The levee holds, or it doesn’t. Somebody on television says it’s a hundred-year flood, which means it’s not supposed to happen for another hundred years, which means everybody acts surprised when it happens again in five. And the people up in Baton Rouge, they make their decisions, and we live with them. That’s how it’s always been.”

She finished her coffee and set the cup on the railing.

“My granddaughter,” she said. “She’s in Houston now. Nursing program. Smart girl. She calls me every Sunday. She says, Grandma, why don’t you come here. I say, baby, I am here. I’ve been here. Where am I going to go that’s more here than here?”

The levee stood behind her, green and enormous. On the other side, the brown water moved south, carrying the topsoil of thirty-one states toward a gulf that was rising to meet it.