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Environmental History of the Mississippi River and Delta

Summary and Keywords

The Mississippi River, the longest in North America, is really two rivers geophysically. The volume is less, the slope steeper, the velocity greater, and the channel straighter in its upper portion than in its lower portion. Below the mouth of the Ohio River, the Mississippi meanders through a continental depression that it has slowly filled with sediment over many millennia. Some limnologists and hydrologists consider the transitional middle portion of the Mississippi, where the waters of its two greatest tributaries, the Missouri and Ohio rivers, join it, to comprise a third river, in terms of its behavioral patterns and stream and floodplain ecologies.

The Mississippi River humans have known, with its two or three distinct sections, is a relatively recent formation. The lower Mississippi only settled into its current formation following the last ice age and the dissipation of water released by receding glaciers. Much of the current river delta is newer still, having taken shape over the last three to five hundred years.

Within the lower section of the Mississippi are two subsections, the meander zone and the delta. Below Cape Girardeau, Missouri, the river passes through Crowley’s Ridge and enters the wide and flat alluvial plain. Here the river meanders in great loops, often doubling back on itself, forming cut offs that, if abandoned by the river, forming lakes. Until modern times, most of the plain, approximately 35,000 square miles, comprised a vast and rich—rich in terms of biomass production—ecological wetland sustained by annual Mississippi River floods that brought not just water, but fertile sediment—topsoil—gathered from across much of the continent. People thrived in the Mississippi River meander zone. Some of the most sophisticated indigenous cultures of North America emerged here. Between Natchez, Mississippi, and Baton Rouge, Louisiana, at Old River Control, the Mississippi begins to fork into distributary channels, the largest of which is the Atchafalaya River. The Mississippi River delta begins here, formed of river sediment accrued upon the continental shelf. In the delta the land is wetter, the ground water table is shallower. Closer to the sea, the water becomes brackish and patterns of river sediment distribution are shaped by ocean tides and waves. The delta is frequently buffeted by hurricanes.

Over the last century and a half people have transformed the lower Mississippi River, principally through the construction of levees and drainage canals that have effectively disconnected the river from the floodplain. The intention has been to dry the land adjacent to the river, to make it useful for agriculture and urban development. However, an unintended effect of flood control and wetland drainage has been to interfere with the flood-pulse process that sustained the lower valley ecology, and with the process of sediment distribution that built the delta and much of the Louisiana coastline. The seriousness of the delta’s deterioration has become especially apparent since Hurricane Katrina, and has moved conservation groups to action. They are pushing politicians and engineers to reconsider their approach to Mississippi River management.

Keywords: flood-pulse, delta, levee, bottomland hardwood forest, flooding, coastal erosion, eutrophication, hypoxic zone, river restoration, disturbance and resilience

Hydrology and Ecology


All rivers are, at bottom, water pulled by gravity downhill against the resistance offered by the land. They all contain a combination of potential energy (water held in position by land) and kinetic energy (water in motion, as it is pulled by gravity) that depends on mass (volume of water) and velocity (steepness of slope). But the simplicity of this truth can be misleading. Rivers, in fact, are a complicated and continually shifting mixture of movement, resistance, and turbulence. Variation can occur from place to place over a river’s length, as changes in slope affect velocity and resistance. They can occur over time, for example, when wet years bring added volumes of rain water. Significant variations can even occur within the same spot in the same river. Water at the surface and at the center, generally speaking, flows fastest and with the greatest force. This is because surface water, being farther above sea level, has a steeper slope than water below it and because water at a river’s center flows more freely than water at the bottom and at the sides, which brushes against land. While a river at any given point may be said to be flowing at a certain speed, no molecule of water within a river flows at a constant speed, but it is always accelerating and decelerating as it moves from surface to bottom and from center to side and as conditions change over the river’s length. Variations in mass, force, and velocity give each river its character or personality and determine its contribution to the ecological systems it helps to sustain (

In the case of the lower Mississippi River, energy of all forms derives from a relatively large volume of water running at a relatively low velocity down a low-grade slope in a wide and shallow channel. Other rivers, the Colorado River for example, have smaller volumes of water falling down steeper slopes at higher velocities. The slope of the upper Mississippi, above the mouths of the Missouri and Ohio Rivers, is greater but the volume lesser than for the lower Mississippi, making it a different river, geophysically speaking.

Environmental History of the Mississippi River and DeltaClick to view larger

Figure 1. Mississippi River Drainage Basin, map courtesy of the U.S. Army Corps of Engineers, public domain.

Much of the river’s energy is spent moving dirt. Off and on for more than a million years, melting glaciers released water down the center of North America, along with millions of tons of glacial sediment. In the spring of 1999, more than 600,000 cubic feet of water flowed every second out of the river and into the Gulf of Mexico, and it was loaded with sediment. The lower Mississippi Valley, from near the mouth of the Ohio River to the Gulf of Mexico, more than 600 miles, is in fact a continental depression and not a true river valley. It has slowly filled with dirt brought there by the Mississippi and its tributaries from across the continent. (Kammerer, 1987;; Durum, Heidel, & Tyson, 1960)

Over the last million years, several episodes of glacial formation and melting have alternately filled and cut the alluvial valley. Melting glaciers unleashed stored water with such force that it initially cut into the valley with several braided streams, which in time slowed and merged to form a single meandering stream that deposited sediment and built up the valley floor. With the coming and going of each new ice age the process of building and cutting repeated. Sea level changes mattered. Rising ocean levels shortened the river, altering slope and velocity. Moreover, the history of the meandering stream was complicated by moments when it divided into multiple meandering streams, each with loop frequencies that differed from that of a single stream. When and why these moments occurred have been difficult to explain. They may in some cases have been connected to changes in tributary flows, and in others may have occurred when the river chanced upon two paths that presented about equal levels of resistance, and it divided and pursued both. Six thousand years of Mississippi River history are captured and frozen in the confusion of former stream courses drawn by geologist Harold Fisk, whose mid-20th-century investigations into the river’s geophysical past continue to inspire research. Agreement on the long-term patterns in the river’s history has come more easily than it has for its short-term history, which has been highly contingent on numerous, often overlooked or misunderstood variables (Fisk, 1944; Saucier, 1994; Saucier, 1996).

The meander zone, below the mouth of the Ohio River, took shape six or seven thousand years ago and is a subsystem within the entire Mississippi River system. It was responsible for sustaining the lower valley environment. The slow, broad, and shallow stream of the lower river deposited on the valley floor layers of fine silt loam topsoil that accumulated to a depth of five feet. In contrast to the earlier, fast-moving streams, the meandering river interacted more with the land beside and below it, which increased friction and converted some kinetic energy into thermal energy. A stream with less kinetic energy is less able to push its way directly across the land, causing it to meander back and forth in search of paths of least resistance. Meanders occurred as the river added to the resistance of the land by adding to the land itself. Sediment accumulations gradually raised the riverbed, lengthened the river, and reduced the slope and thereby reduced the river’s velocity. Along the river’s edge deposits of sediment accumulated, forming natural levees that like dams held the water within the channel. Both actions converted a proportion of the river’s kinetic energy into the potential energy of water held back against the force of gravity, until moments when, squeezed by land of the river’s own making, stored potential energy converted back into kinetic energy and the river burst out of its banks and across dry land. As floodwaters spread out across the land, kinetic energy converted back into the potential energy of water held in place by the land in lakes and swamps. Erosion and deposition—the process is one of continual dam building and dam breaking, blocking the river here, opening a path there, forcing the river into its looping motion as it meanders to the sea. Constant change, building, breaking, and the abrupt conversion of one form of energy into another, all within a stable system, has characterized the lower Mississippi River for several thousand years, since the formation of a single, meandering stream (Arthur & Strom, 1998;

Wherever the river abandoned its channel or cut a new one, it left water on the land. The many oxbow lakes that line the river are former meander loops. Flood and rain water collected in low lying areas, trapped behind the same natural levees that had helped propel the river onto the land in the first place. Swamps formed, and when they became full enough, they overflowed into streams, creeks, and bayous that ran parallel to the main river channel until they found a low point in the natural levee where they could rejoin it. The river wet the land regularly in a pattern that river ecologists call the flood pulse, implying constant motion and energy (Saucier, 1994).

Meander Zone Ecology

Until recent times, the meander zone of the lower Mississippi Valley comprised a vast ecological wetland, one of the largest in the world, approximately 35,000 square miles of water and dirt in various proportions ranging from the wet dirt of the floodplain to the dirty water of the Mississippi River. Much of the lower valley lay permanently wet, and what passed for dry land—a relative term in this context—were the few places that stayed clear of water for a mere ten days of each growing season, which was sufficient time for certain species of hardwood trees to take root. Water and dirt—mud—nourished a forest of water and laurel oak, ash, hickory, tupelo, bald cypress, and sweet gum, to name only the most prominent trees. Lakes, swamps, and sandy islands thickly matted with cane broke up the forest cover into a quilt stitched of blue and light-green patches. Numerous species of animals lived in this wet environment. Lakes and streams teemed with fish, shellfish, reptiles, and amphibians. The wetland ecology produced astonishingly high volumes of plant and animal life, or biomass. Some lakes, for example, supported 800 pounds of fish per surface acre of water, and there were more than 35 million acres of water and wetlands in the lower Mississippi Valley (Lowery et al., 1987; Schramm, Jr., 2004; Lucas & Powell, 1992; Dahl, 1990).

Fish and shellfish were food for raccoons, otters, muskrats, opossums, and other small mammals that also ate grubs, insects, and the eggs of waterfowl. Great flocks of birds nested in the valley. Many more passed through, making the valley the primary flyway for North America’s migratory bird populations. A few larger animals, such as white-tailed deer and black bears, moved through the wetlands. In general, however, the lower valley was a haven for smaller creatures that thrived in a wet environment not favored by large predators (Van der Valk, 2006; Amant, 1959; Gardener & Oliver, 2005; Jeter & Williams, Jr., 1989).

At the valley’s edges the soil quality changed, as did the varieties of plants and animals living upon it. To the northwest into the Ozark and Ouachita hills, and to the east along the bluffs that followed the river from Memphis to Baton Rouge, cypress, tupelo, and sweet gum gave way to white oak, walnut, magnolia, and beech, species more suited to drier, more acidic soils. West of the lowest reaches of the valley, in what is now east Texas and west Louisiana, longleaf pine, post oak, and black land prairie typical of the gulf coastal flood plain extended as far north as the Red River. The frontiers between ecological zones of the wet valley bottom and drier uplands at the valley’s edges formed ecotones in which plant and animal life were often especially abundant precisely because of the blending of wet and dry land. For example, many white-tailed deer typically spent the autumn and winter seasons in the uplands mating and browsing on acorns, but they gave birth and raised young during the spring in the safety of bottomland thickets (Jeter & Williams, Jr., 1989; Smith, 1974).

The Mississippi River Delta

Below the meander zone, near the Gulf, is the Mississippi River’s delta. (The river’s delta is not to be confused with The Delta, the popular name for the floodplain of northwestern Mississippi and eastern Arkansas.)

Environmental History of the Mississippi River and DeltaClick to view larger

Figure 2. Mississippi River Sediment Plume, image courtesy of NASA, public domain.

Each year since the end of the last ice age the river has deposited 100 to 300 million tons of dirt on the coastal shelf, building the delta and the lower quarter of Louisiana. The river’s course in the delta is very unstable because of the resistance of sediment deposits, as well as wind and waves at the coast. Avulsion, or channel-switching, is normal. In addition to the current Balize Delta, there have been six deltaic lobes. When the Mississippi River first began to settle into a single meandering stream, approximately 7,000 years ago, it also began to build its first delta. Approximately 5,000 years ago, the river jumped to the east and began a new delta. It switched three more times, back west, then east, west again down Bayou La Fourche, before turning down its current route into Plaquemines Parish, just upriver from the present-day delta. An eighth delta is emerging in Atchafalaya Bay, atop the remains of the first delta.

The delta was home to the largest saltwater marsh in the United States, a vast expanse of cord grass savannah and coastal estuaries full of fish, shellfish, birds, and small mammals, dotted by a few ridges and islands of slightly higher ground, some high enough to sustain oak groves. Farther inland savannah gives way to cypress forest and freshwater marsh. It was sculpted by the river in interaction with the sea and with the annual hurricanes for which the Gulf of Mexico is well known (Cronk & Fennessy, 2001); Kolb & Lopik, 1966; Penfound & Hathaway, 1938; Lowery, 1974; Palmisano, 1972; Neill & Deegan, 1986).

Altogether, the Mississippi Valley and the river delta comprised some of the richest and wettest land in North America and perhaps the world, rich certainly if measured in environmental terms.

People and the Mississippi River

Human Adaptations to the Floodplain Environment

People lived within the unfolding natural history of the lower Mississippi Valley for more than ten thousand years, contributing to but without significantly altering its physical processes. The people of the Plaquemine Culture and their lower valley predecessors lived primarily off fish and wetland animals, as well as nuts, fruits, and wild grains gathered from the forest; only secondarily did they depend on corn. They fished with twine nets weighted with stone plummets and suspended with floats made of wild gourds. They fashioned lightweight boats that moved through waterways quickly and which they maneuvered skillfully. Their earthen mounds provided refuge during floods, emphasizing their incorporation of the wetlands into their cultures. The mounds were not used as dry land for crops; rather, they were staging areas from which they launched forays into the swamps. Indeed, in light of the remarkable architectural achievements in the lower valley, earthen embankments and other flood control technologies were conspicuously absent. Instead of developing technologies to keep themselves and their settlements dry, native peoples in the lower valley adapted to the wetland environment (Milanich, 1991; Fritz, 2000; Walker, 1936).

The question of whether indigenous people could have prevented floods in the areas where they settled, if they possessed the technological means of doing so, remains open. They were very capable of sophisticated engineering and of organizing the labor necessary to move tremendous amounts of earth. However, they did not construct earthen levees. Instead, when the river rose, they sought refuge on high ground, perhaps on mounds, but more likely in upland areas. Then, as floodwaters receded, they returned to live off wetland plants and animals.

Initially, Europeans adapted to floods, but out of necessity rather than choice. European cities were built on dry land, or else on drained, filled, and otherwise reclaimed lands. They practiced dry agriculture, relying on grains, principally wheat, which were far from flood resistant. However, in the lowlands of the Mississippi Valley, they learned to adapt to what was for them a foreign environment, foreign in large part because it was wet. They built homes on pillars, and in New Orleans, those who could afford to do so built an upper story for refuge during floods. The French tried to cultivate wheat in the Mississippi River delta, with no success in the wet soil and humid air. They did succeed at cultivating wetland rice, a grain they were familiar with, as were many enslaved African laborers. In France, rice was a common substitute for wheat, especially during lent. It had been planted in the very south of France perhaps since Roman times. In parts of West Africa, people had for millennia domesticated and planted in wetland areas a native variety of rice, thoroughly incorporating it into their cuisine and economy. The French added to their own knowledge by appropriating African expertise with rice and with the management of water in wetland fields. In the 21st century, rice remains a staple of black and white Louisianans. In 18th-century Louisiana, rice marked another adaptation by the French to the environmental reality of the Mississippi Valley and delta (Morris, 2012).

In marked contrast to native peoples, the French and their successors, the Spanish, English, and European Americans, never stopped trying to adapt the river to their purposes, even when they clearly lacked the human and material resources to stop the river’s normal flood patterns.

Early Modifications of the Mississippi River

In 1719, a flood brought work on the construction of the new town of New Orleans to a standstill. Many thought the site too wet for settlement and urged relocation. Instead, the colonial governor ordered the construction of drainage ditches and a levee (from the French verb lever, to raise, and the noun levée, a raising or rising) to keep New Orleans dry. Landowners in the vicinity of New Orleans followed suit and put thousands of enslaved Africans to work on levees. In 1725, colonial authorities required a minimum three-foot levee along the river, which raised river levels by constricting water, which in turn necessitated still higher levees. By 1732, levees perhaps four feet high lined both sides of the river for nearly fifty miles. By 1752, the network was extended perhaps another ten miles. Over the years, the levees grew higher and flooding remained a problem. By the late 18th century, administrators authorized a system of levees, drainage canals, and even some wind operated pumps, constructed and maintained largely by enslaved African laborers, that offered a modicum of control over the river (Superior Council; Harrison, 1961; Morris, 2012).

In 1797, Spanish colonial administrators and engineers, who succeeded the French, entertained a proposal to construct a series of canals that would cut through meander loops. This would shorten the river and hasten the flow of water to the gulf, reducing flood risk. In addition, cutoffs would shorten transportation time between New Orleans and upriver settlements such as Natchez. The proposed canals were to be near the confluence of three large waterways, the Mississippi, the Red, and the Atchafalaya rivers. How they would react to the proposed modifications was anybody’s guess. In the end, the governor decided to leave well enough alone (Morris, 2012).

Prior to 1803 and the purchase of Louisiana by the United States, administrators and riverside landowners thought of the river not so much in terms of alteration as accommodation, even though by constructing levees they were in fact altering, if modestly, patterns of flooding, erosion, and deposition. Since then, governing authorities and individual landowners in the Mississippi Valley have endeavored to accommodate the Mississippi River to human needs. They have reconfigured it by altering the balance between potential and kinetic energy and by redirecting the work of that energy. During the 19th century, people transformed the valley, draining it of water, clearing the land of forest, drying the soil, and planting cotton, which, unlike rice, cannot tolerate flooding in the least.

In 1831, Henry Shreve and the U.S. Army Corps of Engineers completed the cutoffs that the Spanish had refrained from undertaking, and as a consequence, water from the Red River began to flow almost entirely into the Mississippi River. Meanwhile driftwood and silt loosened from upriver locations by landowners as they cleared forests for farms and plantations, clogged the Atchafalaya River, which Shreve managed to clear, but this in turn drew water from the Red River away from the Mississippi. As the Red and Atchafalaya became a single stream, the confluence of the Red and Mississippi rivers began to fill with sediment, which interfered with steamboat navigation (Morris, 2012).

Henry Shreve is best known for his efforts to clear the Mississippi and other rivers of debris, to facilitate steamboat passage primarily so that cotton could more easily and cheaply be shipped from plantation landings and river towns to New Orleans and thence overseas. Agriculture, and in particular, cotton cultivation, was a powerful incentive for modifying the lower Mississippi River (Gudmestad, 2011; Kelman, 2000).

In the 19th and 20th centuries, people reconfigured the Mississippi River, especially in the meander zone, by separating water and land and what was wet from what was dry. Landowners, or more accurately, their hired and enslaved laborers, cleared, drained, and dried the land, and then they planted crops ill-adapted to the lower valley’s formerly wet environment. Levees and other flood control structures kept the river off dry land. The pace of clearing, draining, and leveeing accelerated at the turn of the 20th century, when the last stands of old growth pine and cypress fell before an onslaught of timber companies with power saws and other machines. Remaining bottomland hardwood forests disappeared soon thereafter, victims of commercial timber operations. In the 20th century, much former wetland and forest, approximately 5000 square miles, was paved over for automobile usage and urban development. Over the last two centuries, Louisiana, Mississippi, and Arkansas have lost nearly 60% of their wetlands (Foley et al., 2004; Lubowski, 2002; Federal Highway Administration; Brown, 2001; Dahl, 1990; Outwater, 1996; McNeill, 2000).

The Role of the U.S. Government

The United States government organized the transformation of the lower Mississippi Valley from wet to dry. At the end of U.S. Civil War, levees along the Mississippi River lay in ruins. Lacking funds to pay for reconstruction, the states of Louisiana, Mississippi, and Arkansas sought Congressional assistance, which took time to negotiate. Reflecting the sentiments of constituents, many members of Congress were reluctant to offer any assistance to the riverside landowners who had participated in a long and bloody war of rebellion. But the argument that the Mississippi River was a vital national resource, primarily for navigation, won out. Navigation proved critical. Whereas Congress was reluctant to use public resources to protect private lands from flooding, Congress had since the nation’s beginnings played an important role in improving navigation. Aware of this fact, politicians who sought flood control declared that the best way to improve navigation would be to build levees. They found an ally in the Army’s Chief of Engineers, Andrew Atkinson Humphreys (Morris, 2012).

Humphreys was the principal author of Report on the Physics and Hydraulics of the Mississippi River (1861), the most detailed study of Mississippi River hydrology to date. It provided all the empirical evidence necessary, he claimed, to prove that levees and levees only could keep the river open to navigation and provide flood control. Levees would contain the river and also deepen it. Opposed to Humphreys and his levees-only approach were scientists who studied meandering rivers systematically, comparatively, and theoretically. Many of their suggestions were based on what they had learned from European rivers and engineers, whereas Humphreys regarded the Mississippi River and the problems it posed as unique. They were deeply skeptical of Humphreys’s plan. They pointed out, for example, that sediment not deposited in the channel, as Humpheys claimed it would not be, would necessarily end up at the mouth of the river, where it would impede navigation. Sediment depositions at the mouth would cause the river to lengthen, which would reduce its slope and slow its velocity. A slower river would then drop more sediment upriver and eventually the very problem Humphreys claimed to solve would return. For a variety of reasons, including his point-by-point rebuttal of his critics, his rank, the appeal of his argument to nationalists who saw America, including its greatest river, as exceptional, and the fact that Humphreys’s plan allowed for piecemeal construction, which budget-conscious politicians liked, the levees-only approach won Congressional support (Morris, 2012).

In 1879, the year of Humphreys’s retirement, Congress established the Mississippi River Commission (MRC) and committed the federal government to aiding the lower valley states in their efforts to control the Mississippi River with levees only. Congress appropriated $50 million and handed oversight of the budget to the MRC. The 1881 River and Harbor Act permitted direct federal assistance for levee construction, putting design and construction in the hands of the army engineers, on the grounds that levees improved navigation primarily, and flood control secondarily. By the end of the century, walls constructed of willow branches, concrete, and earth separated the river from its floodplain. Not until the flood of 1917 did Congress at last drop all pretenses that levees were for commerce and navigation rather than for flood control. The Flood Control Act of 1917 provided for up to $45 million, with matching funds to come from each state, “for controlling the floods and for the general improvement of the Mississippi River” (Morris, 2012).

On April 16, 1927, the Mississippi River broke through the levee at Dorena, Missouri, not far below Cairo. Three days later and on the same side of the river, the levee at New Madrid gave way. On April 21, the river broke through at Mounds Landing, near Greenville, Mississippi, killing more than 100 African Americans as they piled sandbags under the pointed guns of the National Guard. On April 29, dynamiting commenced at the Caernarvon levee, in Plaquemines Parish, to relieve pressure on the levee at New Orleans, but at the cost of the livelihood of downriver rice farmers and muskrat trappers. By the end of the month, water inundated 26,000 square miles and displaced more than one million refugees. The 1927 flood was, and by some measures remains, the nation’s greatest natural disaster (Barry, 1997).

In 1928 Congress appropriated funds for the reconstruction of the levees, including the section intentionally blown at Caernarvon, and committed itself to a new long-term project, which became known as the Mississippi River and Tributaries Project, or Project Flood. The new project reviewed and revised the levees-only approach, with the MRC agreeing to build the Bonnet Carré Spillway in Louisiana and the Bird’s Point–New Madrid Floodway in Missouri, both of which would permit the controlled release of water from the Mississippi to relieve pressure on levees. Eventually, engineers added a third spillway, at Morganza, Louisiana. The 1928 legislation also authorized the Army Corps of Engineers to maintain a channel depth of twelve feet, although that has been achieved only partially. In the 1930s, the Corps completed several cut-offs to shorten the river between Memphis and Vicksburg. A shorter stream would flow faster, and whisk floodwaters away. The 1928 act also authorized research into ways “proper forestry practice” might reduce flooding. These adjustments to the system were intended to make the levees work, not to replace them. Indeed, there were to be no outlets on the entire east bank of the river above Baton Rouge, nor were any outlets to interfere with the project of “raising, strengthening, and enlarging the levees on the east side of the river” (USACE River and Tributaries; Wohl, 2004).

When the United States entered World War II, more than 1600 miles of levees several stories high and at their base the width of a football field lined most of the Mississippi River below Cape Girardeau, Missouri. Set back from the channel, they were designed to contain floodwaters. The river still floods, but since the 1930s, in a more controlled manner. For example, in 2011 engineers responded, not without political controversy, to a very serious rise in the river by releasing water through designated spillways, relieving pressure on the levees. Levees separated land and river, impeding their familiar ways of interacting, interfering with the flood-pulse pattern that sustained the valley’s ecology.

Nevertheless, river and land continue to interact, albeit in sometimes unexpected ways. Forests, meadows, and marshes absorb, filter, and release rainwater slowly into surface (river, lake, ocean) and ground (aquifer) water systems, or else into the air through evaporation. Clearing, draining, and tilling has reduced the land’s capacity to retain moisture and to resist erosion. Fields, especially during times in the agricultural cycle when they are bare of plants that would slow the movement of running water, often shed water if not as quickly as a parking lot, nevertheless, too quickly to be adequately absorbed. Roads, roofs, storm sewers, and other impermeable surfaces inhibit or entirely prevent water from seeping into the soil, much less into groundwater systems. In such places runoff can enter rivers too quickly to be accommodated by them, causing sudden floods. In much of the lower valley the soil is drier than it used to be, although it is, paradoxically, more prone to flooding from heavy rains. Like a dry sponge, dry land is not good at absorbing water. In some places, the land is wetter than it used to be. A rise in the Mississippi always pushed water up its tributaries and onto the floodplain. However, backwater rises tended to be brief, draining back into the river system once it fell below flood stage. Levees, however, interfered with this ebb-and-flow process, forcing water to rise far up tributaries, and then trapping water that spilled onto the floodplain. For example, the construction of intersecting levee systems at the confluence of the Mississippi and Yazoo rivers in south Issaquena County, Mississippi, trapped rainwater, as well as river water that topped or broke through levees up stream, much to the frustration of land owners. The problem was so acute that the Flood Control Act of 1941 authorized a plan put forward by the Corps of Engineers, to pump trapped backwater over the levees and into the Yazoo River. For complicated political reasons, including cost, and more recently, a conservation movement to preserve wetlands, the Yazoo Backwater Area Pumps Project has never been completed, although versions of it remain on Corps drawing boards (Dahl et al., 2009).

Engineering has altered patterns of erosion and sediment desposition. Louisiana has been losing its coastal marshes almost as quickly as it has been losing its interior wetlands. The phenomenon of coastal degradation is relatively recent. In the 19th century, the problem was too much, not too little, river sediment. In particular, sandbars at the mouths of the river’s outlets at the Gulf of Mexico frustrated navigation (Figure 2).

In 1875, Congress authorized James Buchanan Eads to begin work on two long jetties at the Mississippi River’s South Pass. Eads promised that by constricting the river and increasing its velocity, the jetties would cause the river to scour its own channel. This was the same argument Humphreys had made when he proposed a “levees-only” means of flood control and navigation improvement. In a clash of egos, however, Humphreys opposed Eads’s jetties. There were some members of Congress who expressed doubt with Eads’s plan, although a commission that reported on European successes with similar structures helped to ease some minds. When Eads proposed not to bill Congress for the jetties, should they fail, Congress allowed him to proceed. By spring of 1879, it was clear that the jetties were working as promised. The channel, only seven-and-a-half feet deep when construction began, had deepened to more than twenty-six feet. A dejected Humphreys retired (Barry, 1997).

At the end of the 19th century, private real-estate developers, as well as the State of Louisiana and the U.S. Congress, invested in reclamation schemes to turn Mississippi delta and Louisiana coastal marshland into farmland. The Louisiana Land Reclamation Company, chartered by the state legislature in 1878, set about draining 13,000 acres in Terrebonne Parish, using steam-powered dredges, plows, and pumps. This land was 18 inches above low tide, and was submerged, barely, during high tide. In 1885, David Montgomery Nesbit, a tidewater Maryland farmer and real estate broker, published a report on tidal marshes in the United States, in which he declared “that the day of unlimited cheap land is passing.” The future of the nation, he claimed, depended on the success with which new land could be made out of wetlands. Nesbit devoted a substantial section of his report to the Louisiana Coast. Nesbit saw coastal lowlands and tidal marshes as spaces for settlement and agriculture, or more simply, as potential lands of opportunity, if only they could be reclaimed—the common word of his day—from the sea, because in their natural state they were not deemed habitable (Harrison & Kollmorgen, 1947; Nesbit, 1885).

Transformation of the Hydrological System

In 2010, the population along Louisiana’s coast from Cameron Parish to St. Bernard Parish was seven times larger than it was is 1890 (three and a half times larger if we do not count Jefferson Parish, which at nearly half a million people and comprising much of suburban New Orleans, is much larger than the other parishes.) This growth was made possible by the reclamation projects Nesbit envisioned (U.S. Census Bureau).

Meanwhile, the land has been disappearing. Mississippi River channel reconfiguration around and below New Orleans has impeded the annual floods that formerly spread sediment across a broad delta and along the coast. The result is, the delta keeps getting longer and thinner. Levees and a straighter, somewhat deeper channel have increased the river’s velocity and force. Sediment carried by the river is shot far out into the Gulf of Mexico, where it drops off the continental shelf and onto the deep-sea floor, rather than collecting along the coast. Encroaching sea water is killing vegetation that would hold sediment in place, further exacerbating the problem of erosion. Coastal ecologies are changing, as are offshore ecologies. Through a process known as eutrophication certain dissolved substances, such as phosphates and nitrates, stimulate the blossoming of algae, great clouds of which annually create hypoxic, or “dead” zones by depleting dissolved oxygen and suffocating fish and shell fish (Blum & Roberts, 2009; Harrison & Kollmorgen, 1947; USACES, 1994; Malakoff, 1998; Driscoll & Schramm, 1997; Allen & Burkett, 1997; USDA, 2006; Coleman, 2003).

Sediment load increased with deforestation and the spread of agriculture. In recent times, however, it has decreased, a consequence of changes in agricultural practices and of dams put in place in many of the Mississippi’s tributaries. As important as the change in quantity of runoff is the change in its quality. Runoff from hard surfaces carries chemicals and all sorts of debris, including paper, plastic, and motor oil, where it mixes in the river with the runoff from farmland. Much of it is toxic (Barbarino et al., 1995; Antweiler et al., 1995; Colten, 2000; EPA, 1998, 2006).

Many human-induced alterations of the river’s physical system stem from the separation of land and water. There has been a separation of change and continuity. To facilitate change on the land, engineers have put the river into a state of suspended animation. Levees hold it in place, preventing it from going where or doing what it wants. It is as if the progress of human history in the lower valley has necessitated the denial or the cessation of the river’s history. The land has been cleared, dried, and planted so that people can take advantage of the rich soil, and yet clearing, drying, and planting has deeply disrupted the system that created and maintained the land in the first place, necessitating all sorts of counter measures to maintain the richness of the land. Separation encourages pollution because it promises that what is dumped into the river will never return to touch the land or the people upon in. Agricultural runoff and industrial waste are tolerated in the river because the river is held at a safe distance from the land. At the same time, separation impedes the natural cleansing process of land/water interaction that occurs when water moves over and through the land to be filtered by it. The water is thus more dangerous, and separation becomes more necessary. Separation necessitates further separation. By the late 20th century, flood control structures offered protection not only from water but from the poisons within it.

Nevertheless, the Mississippi River remains a system of shifting kinetic and potential energy. Sediment in the river offers evidence that land and water continue to interact. The river’s toxic sediment load acknowledges what the levees repress, that land and water have remained connected and in constant interaction. So, too, do periodic floods offer reminders that land and water cannot be kept permanently apart. Much of what is on the land eventually ends up in the river, and every so often, the river ends up on the land. That has been the case for thousands of years. Only in the last century have people lived in the lower valley as though land and river can and ought to be kept apart.

The Future of the Mississippi


The flooding of New Orleans in 2005 following Hurricane Katrina drew national attention to the failed history of Mississippi River flood control. Storm surges pushed water up the river from the Gulf of Mexico and from Lake Pontchartrain through drainage canals and into the city. Riverside control structures held, however, as they have held in the lower valley, despite dire predictions, since the reconstruction of the levees following the great flood of 1927 (Figure 1). In 1973 and 1993 there were serious floods upriver, in Missouri and Illinois. However, the Katrina disaster drew attention to Louisiana’s receding coastline, which for centuries has provided a natural barrier against hurricanes, but which has suffered from the reconfiguration of the river, and from infrastructural development for Louisiana’s coastal oil and gas industry. A greater awareness of environmental change among many Americans living in an era of human-induced climate change and a corresponding skepticism of technological fixes has eroded political support for flood control. There is a growing demand for the dismantling of levees and the restoration of wetland, not merely in the delta and coastal region, but along the length of the meander zone.

The political feasibility of floodplain restoration grows as rural populations move elsewhere. During the rise of 2011, the Army Corps of Engineers opted to relieve pressure on levees protecting the Illinois town of Cairo by flooding farmland in nearby Missouri. Thus far, efforts to authorize and fund reconstruction of the levee at New Madrid, Missouri, opened by the Corps of Engineers in 2011, have stalled in the face of opposition led by conservation and restoration groups. Mississippi River restoration is a concept whose time has come. Aging levees that for more than a half a century have protected small communities, such as Wolf Lake, in Union County, Illinois, may be dismantled. Following the 1993 flood, several Missouri and Illinois towns relocated to higher ground. Down river, conservation groups are restoring a forested floodplain habitat upon the batture, the ribbon of land between the levees and the river. Support for the Yazoo Pumps project is weakening, having failed to convince the Fifth Circuit Court of Appeals to overturn a block on the project by the EPA. In the Mississippi River delta, engineers, scientists, charities, and nonprofit organizations have formed the Restore the Mississippi River Delta coalition. In 2014, the Coalition to Restore Coastal Louisiana, working with the Delta coalition and other conservation groups, and with the City of New Orleans and the State of Louisiana, put forward a master plan to dredge and divert sediment flows in an effort to stem erosion of the delta and the Louisiana coastline. The LaBranche Marsh, near New Orleans, offers an example of successful wetland restoration. Diverted sediment held in place by recycled Christmas trees has restored hundreds of acres. Elsewhere in the delta and along the coast, restoration projects have proven difficult to initiate, in part because they require the relocation of entire delta communities (Dalbom et al., 2014).

Even along the Upper Mississippi River, near the Twin Cities, restoration projects are underway, where the U.S. Army Corps of Engineers is constructing islands and restoring wetland fish and waterfowl habitat. As the Lower Mississippi River Conservation Committee (LMRCC) has explained, “habitat enhancement, rehabilitation and restoration of the Lower Mississippi River and its floodplain” requires the restoration of connections between river and floodplain, and between river and people that the levees severed. For the time being, LMRCC concentrates its restoration efforts primarily on the “relatively intact ecosystems” of the batture, which is politically pragmatic because no levees need be dismantled, although the political climate is changing in favor of more extensive restoration efforts (LMRCC, 2015; Restore the Mississippi River Delta Coalition, 2016).

Disturbance and Resilience

The concept of restoration derives from the very concepts used by scientists and engineers a century ago when they sought to control flooding by separating water and land, wet and dry. The first ecologists to study floodplain habitats wrote of floods as disturbances, much as forest ecologists from the same era thought of fire as disturbances, as intrusive forces, whether set by nature or by people, that upset ecological equilibrium. Such a view influenced engineers and politicians, who argued that levees helped to conserve floodplain ecologies even as they prevented floods from disturbing human activities. By separating rivers from their floodplains, levees could be construed as conservation structures (Morris, 2016).

Later in the 20th century, ecologists Wolfgang Junk, Peter Bayley, and Richard E. Sparks noted beneficial effects of seasonal floods on terrestrial life, and proposed the flood-pulse theory of floodplain ecology. At about the same time, the periodic failure of flood control structures along the Mississippi, as well as the increasingly obvious long-term detrimental effects of levees on the delta and the Louisiana coastline, generated a new conservation movement aimed at opening levees, at least in some places, to restore connections between river and land. Restoration groups such as the Coalition to Restore Coast Louisiana tend to regard levees and other flood-control structures as disturbances that weaken the natural resilience of ecosystems. Whereas natural disturbances, such as flooding, can strengthen the ability of an ecosystem to rebound (resilience), anthropogenic disturbances can have the opposite effect. Opening the levees near New Orleans, and even permitting controlled flooding in parts of the city will stem coastal erosion, indeed, will encourage sediment deposition. Land formation will, in turn, protect the city from storm surges, in addition to providing better habitat for coastal animal life, fisheries in particular.

The Mississippi River can frustrate restoration plans, just as it frustrated centuries of flood control efforts. The delta has always changed, moved, eroded here and accrued there. The levees that seem to have caused the unwanted erosion of the coastline are also the levees that have kept the river in the channel that flows past New Orleans. Without the levees, the mouth of the river would be far to the west of its present location, and the delta around New Orleans, and the city itself, would go the way of the Chandeleur Islands, a former delta that long ago sunk into the sea. Since the 1830s and the days of Henry Shreve, the engineer who disturbed the delicate balance between the Mississippi, Red, and Atchafalaya rivers, the Mississippi has sought to switch its main channel, near the old river bend that Shreve cut off, and from there to flow down to the gulf by way of the shorter, steeper Atchafalaya. In 1954 the Corps of Engineers received authorization to construct the Old River Control Structure, a complicated device designed to permit sufficient water to flow from the Mississippi into the Atchafalaya Basin to maintain a barge channel and to scour it of Mississippi River silt, without allowing the Atchafalaya to capture all of the big river, for that would be an irreparable disaster. The near failure in 1973 of the Old River Control Structure was the subject of a long essay by nature writer John McPhee, who argued that the complete turn of the Mississippi down the Atchafalaya was inevitable. Decades later, the situation remains precarious. If, or when, the river switches channels, Baton Rouge, New Orleans, and all the industries between will no longer be on the Mississippi River. Moreover, with no Mississippi River sediment to prop up the delta around New Orleans, most if not all the city will sink into the sea, while a new delta will emerge at the mouth of the Atchafalaya. Some levees and river control structures need to remain in place if the city is to survive, even as other levees will need to be dismantled to help restore the delta and to make it more resilient against storms, rising oceans, and levees (Coastal Protection and Restoration Authority, 2012; Day et al., 2014; Herbert & Muth, 2016; McPhee, 1989; Reuss, 1998).

The Example of Reelfoot, Moon, and Eagle Lakes

The complexities of managing the Mississippi River system, whether by separating water and land, or by facilitating their interaction, is clear in many places along the river, but the best example may be the Reelfoot Lake region of Tennessee. In 1992 the National Research Council Committee on Restoration of Aquatic Ecosystems identified Reelfoot Lake, Tennessee, as a lake of national significance that was, in the committee’s word, “impaired.” Agricultural expansion in the vicinity of the lake had hastened sedimentation, reducing the lake to one quarter its original size. Chemical fertilizers in runoff caused excessive weed and algae growth, which reduced levels of dissolved oxygen and harmed fish populations. Fewer fish meant fewer herons and egrets. Agricultural pesticides harmed ospreys and bald eagles. “Rough plants dominate” and “nuisance plants are proliferating,” reported environmental scientists, who concluded that “The lake will soon become marshland.” This was bad news for the economy of this poor, rural region, which stood to lose ten million dollars annually spent by boaters and sport fishers from Memphis, Nashville, and southern Illinois. Restoration of the lake would require changes in area land management and an investment of tens of millions of dollars (National Research Council, 1992; Duda et al., 1984).

What the authors of the study did not note was that the state to which they sought to restore Reelfoot existed only in fantasy. Of concern to the Committee on Restoration of Aquatic Ecosystems was the silting-in of the lake. Silting is a natural process of lakes on the Mississippi floodplain. Portions of Reelfoot sit in an old river meander that had once been lake but which long ago filled with silt, until the earthquakes in 1811 and 1812 dammed the Reelfoot River to make it into lake once again. Of course, the driving force for restoration was not concern for fish and water fowl populations, but the local economy. Reelfoot Lake will one day be “too shallow for recreational purposes” (National Research Council, 1992).

Inspiration for restorations efforts at Reelfoot could be found at several other riverside lakes popular with sportfishers. Moon Lake was created by a cutoff late in the 18th century. At the time of the Civil War, a small channel connected the lake to the Mississippi River, and kept the lake from silting. In the early 20th century, Moon Lake developed into a prime fishing spot, with Mississippi paddlefish among those most prized by fishers, both sport and commercial. However, once levees cut the lake off from the river, it began to fill with silt, which would have happened in any case, except that by the 1990s there was much community demand for lake restoration, much of which has been met. A similar history has unfolded at Eagle Lake, near Vicksburg, formed in 1866 when the Mississippi River cut across Eagle Bend. A portion of the original lake has filled with silt, but what remains is carefully managed. The lake is protected by levees and controlled streams. In this manner, lake water is kept relatively clear of silt, in the interest of sport fishing and real estate development (MEDQ, 2003).

Hydrological and ecological restoration of the lower Mississippi River and floodplain may require as much human management and scientific expertise as has flood control. The legacy of the last several centuries of history along the river may be that people cannot, and perhaps should not, cease their interaction and even their interference with the river. Nevertheless, restoration, rather than transformation, represents an important change in the relationship between people and the Mississippi River.


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