Taming the River to Let In the Sea
In February 2005, the late Shea Penland, Director of the Pontchartrain Institute for Environmental Sciences at the University of New Orleans, and the University's Braunstein Professor of Petroleum Geology, outlined the threat of hurricanes and catastrophic flooding to the city of New Orleans and the surrounding Mississippi Delta region. With Hurricane Katrina, the full horror of that threat was realized. Behind the tragedy lay both natural trends and the impact of human settlement and engineering. Penland's article, reproduced below, explored those factors and provides a guide to the obstacles that still must be addressed as the devastated region is rebuilt.
If you live in Louisiana and dont know how to swim, now might be a good time to learn. The state is rapidly disappearing into the Gulf of Mexico. As a result of hundreds of years of natural-resource exploitation and modifications to the flow of the Mississippi River, whose silty waters created the delta region of southern Louisiana, the states coast lost more than 1,900 square miles of land in the twentieth century alone. At the current rate of loss in Louisiana, an area of wetlands the size of the Baltimore-Washington, D.C., metropolitan area will disappear by 2050. Without putting a massive program of ecological restoration into effect immediately, the fertile crescent of the Mississippi River is doomed to wash away sometime in this century.
Habitable land has always been a critical issue in coastal Louisiana. Much of the state lies only a few feet above sea level; the highest elevation in Louisiana is only 535 feet. Much of the city of New Orleans is actually below the level of the Gulf of Mexico. No wonder, then, that the earliest European explorers, colonists, and entrepreneurs became preoccupied with taming the Mississippi. Wherever people settled, they built levees, channels, and canals to control the floods; they reclaimed land from the bottoms of swamps and running rivers; and they did whatever else they could to harvest the bounty of Louisianas deltaic Eden.
The Mississippi and other rivers, of course, are not the only threat to Louisianas lowlands. Every year hurricanes pose a threat from the Gulf of Mexico. The accompanying storm surges cause local, short-term flooding, but they also lead to permanent erosion of the coastal marshes and barrier islands in the Gulf, which provide the only protection for the inhabited lowlands farther inland. Louisianans have focused on river flooding for hundreds of years, yet only in the mid-1970s did the state begin to take the coastal erosion problem seriously.
The breakdown of the marshes and beaches coupled with the drainage of reclaimed lowlands remains a disaster in the making. New Orleanss defenses would simply crumble if a truly enormous storm lingered over the city for long: a storm the size of, say, Hurricane Ivan, which made landfall along the Gulf coast of Alabama last fall, roughly 150 miles to the east.
Important as they are, though, beach erosion and flooding are still not the heart of the problem facing Louisiana: subsidence of the delta plain is. Before the levees were built to channel and control the Mississippi and other nearby rivers, floodwaters would spread out and slow down as they flowed over the delta. When the flow slowed, the river would deposit its burden of silt, forming a new layer of earth. But the levees, which now constrict floods along a 1,200-mile corridor of the Mississippi, keep the floodwaters from spreading across the delta. Instead, the river-borne silt is lost off the edge of the continental shelf.
The delta, primarily mud that already filled the Mississippi River valley before the levees were built, is continuously being compacted under its own weight. As it compacts, it loses elevation, and without floods, no new sediments can arrive to build the land back up. In the past several hundred years, subsidence rates have ranged from a foot to four and a half feet per century.
Compounding the risk of catastrophic flooding is global climate change. Many climatologists expect such change to cause hurricanes even more frequent and more violent than the ones of the past several years. Sea levels are expected to rise by ten to twenty inches. As Louisianas marshes and barrier islands sink farther into the sea, the people of Louisiana could find themselves exposed to the elements. But the present trends and
The threatened collapse of coastal Louisiana has been centuries, even millennia, in the making. Eighteen thousand years ago, with the end of the last ice age, sea levels began to rise dramatically. For thousands of years the great glaciers that had formed in the preceding era melted into the ocean, until, four thousand years ago, the sea level stabilized. But the Mississippi now met the sea in what had been its old valley. The river water, halted in its course by the Gulf of Mexico, no longer had the energy to carry its sediment. The sediment, falling out of the flow, began filling in the ancient river valley. The result was a subsidence-prone delta that could maintain its elevation only so long as sediment from upstream reached the delta plain each year.
Meanwhile, for thousands of years, the Mississippi Delta has undergone a process known as delta-lobe switching. The path the river takes to the Gulf is constantly changing, because the river is continuously drawn along the most efficient path to the Gulf [see map on opposite page]. Thus time and again the delta forms and reforms. By roughly four thousand years ago, the St. Bernard delta lobe was building up to the east of New Orleans and cut off three bays from the sea; those became lakes Maurepas, Pontchartrain, and Borgne [see map above]. The lobe terminated at the Chandeleur Islands, to the east. Geologically, though, that drainage did not last long. By roughly three thousand years ago, the Mississippi was probably also entering the Gulf via the Lafourche lobe,
In the past thousand years the volume of flow through the St. Bernard and Lafourche delta lobes has waned significantly. Their distributaries shifted to a more efficient course through what is now the main stem of the Mississippi, downstream from New Orleans. But that course is doubtless no more permanent than the others.
As I noted earlier, ever since European settlers began living in the Mississippi River valley, they have been building levees to protect themselvesboth their farmland and their citiesfrom the rivers floods. By 1812 the levees on the east bank extended 135 miles, from New Orleans to Baton Rouge. The levees on the west extended 210 miles, north to the Red River.
Unfortunately, levee construction during that early period of flood control was of poor quality. The levees were narrow, low, vulnerable to destruction by large floods, and generally ineffective at controlling the river. The shoddy workmanship, combined with severe flooding in the first half of the nineteenth century and the growth of New Orleans and surrounding communities, compelled the U.S. Congress to act. The Swamp Land Act of 1849 authorized Louisiana to create a system of levee districts. Each district received donated federal land that it could sell; the proceeds were to finance levee construction and land reclamation.
The American Civil War, and severe floods in 1862, 1865, and 1867, undid much of the work done under the Swamp Land Act. In 1879 Congress made the U.S. Army Corps of Engineers the leader of a new agency charged with
A further problem became apparent in the early 1940s. At that time the Mississippi River Commission engaged Harold N. Fisk, a geologist at Louisiana State University, and a team of geographers and geologists to investigate delta-lobe switching by the Mississippi. Fisk and his colleagues realized that the Mississippi River would soon shift down the shorter course of the Atchafalaya River to the Gulf of Mexico. In response, the Corps of Engineers built a massive concrete structure known as the Old River Control Structure, at the confluence of the Red and Mississippi rivers, where the Atchafalaya begins. This structure controls the volume of water that flows down the Mississippi, allowing no more than 30 percent of the flow to enter the Atchafalaya. The remaining 70 percent continues past Baton Rouge and New Orleans to the Mississippis present delta in the Gulf. With the completion of the Old River Control Structure, the Mississippi River appeared tamed.
It was obvious, even in the 1950s, that the sediments of the historic spring floods no longer reached their natural resting grounds in levees, swamps, and marshes. At the time, that seemed a blessing. The primary effect, however, was to restrict sedimentary land buildup to two isolated locations on the coast: at Head of Passes, seventy miles southeast of New Orleans, where the Mississippi River reaches the Gulf, and at the Atchafalaya River outlets, south of Morgan City. Elsewhere across Louisiana, coastal land loss continued to worsen. Flood control had set the stage for disaster.
Initially, no one viewed coastal land loss as a problem as severe as flooding. Hurricanes, though causes of flooding and locally catastrophic erosion, did not immediately affect state or national coastal policy. The first official recognition that beach erosion in Louisiana needed higher-level attention came with a Corps of Engineers report on Grand Isle, the states only developed barrier island.
The state did not sit up and take notice, however, until shoreline erosion began to threaten state coffers in the 1950s. Controversy arose over the ownership of mineral rights under the Gulf of Mexico, between the offshore boundary of Louisiana and the water bottom claimed by the federal government. The office of the Louisiana attorney general, seeking to garner support for offshore claims, conducted the first comprehensive analysis of shoreline erosion for the period from 1932 until 1954. The survey showed that Louisianas Gulf shoreline had receded by an average rate of six and a half feet per year. By 1969 the rate of erosion had risen to seventeen feet per year.
Louisiana soon had more bad news. In 1970 a report noted that the state had lost interior coastal lands at a rate of almost six square miles a year between the 1890s and 1930s. Furthermore, the rate had accelerated to more than sixteen square miles a year by the 1950s. The U.S. Fish and Wildlife Service found that between 1955 and 1978, Louisiana lost more than thirty-five square miles a year.
Such conditions put human settlements at great risk from encroaching water. To combat it, New Orleans and other communities are protected by two kinds of levee. One defends against the Mississippis annual floods; the other protects against deadly hurricane storm surges. Meanwhile, without the floods,
The downside of flood control is not limited to the natural dispersal of sediments. It also interferes with the dispersal of nutrients across the delta. Even before the twentieth century, early conservationists noted that the river alterations were causing entire ecosystems in areas away from the main stem of the river to decline. Years after the levees and spillways were completed, investigators from the Louisiana Universities Marine Consortium discovered a dead zone of waterat times as large as Massachusettsspreading over the Gulf of Mexico from the shoreline at the mouth of the Mississippi. Devoid of dissolved oxygen, the dead zone owed its existence to massive flows of fertilizers collected by the Mississippi and its tributaries.
By the early 1980s, despite the signs of impending disaster (many of which had originated out of the decisions made by the federal government), federal and state agencies were still reluctant to attempt any kind of restoration. So locals acted first. In 1984, the frustrated government of coastal Terrebonne Parish, some forty miles southwest of New Orleans, appropriated $1 million for the first barrier-island restoration project in Louisiana, at Isles Dernières, under the direction of Robert S. Jones, the parish engineer and a leader in barrier-island restoration.
In 1989, finally prodded into action, the Louisiana legislature established the Louisiana Wetlands Conservation Authority, and Congress subsequently passed the Coastal Wetlands Planning, Protection, and Restoration Act of 1990 (CWPPRA). By that time the combined funding of various state and federal coastal restoration programs in Louisiana had reached more than $50 million a year.
Throwing money at a problem is one thing; spending it wisely is another. But the restoration projects envisioned seemed to incorporate the best thinking about how to address the present problems. The projects included the diversion of freshwater and its sediment from the Mississippi into marshes, the creation and protection of marshes, shoreline erosion control, and the restoration of barrier islands.
One of the first restorations was the Caernarvon Freshwater Diversion Project, which began operation in 1991. Planned prior to CWPPRA, the project called for discharging as many as 80,000 gallons of freshwater per second into the swamps, marshes, and shallow bays east of the Mississippi River and downstream from New Orleans, in Saint Bernard and Plaquemines parishes. That lowland area had been losing as much as a thousand acres a year. The Caernarvon project consisted of a set of diversion gates built through the existing flood-control levees; the flow through the gates was intended to mimic the natural over-bank flooding that built the delta.
Since 1991 the Caernarvon project has become a model that has afforded valuable practical experience with restoration techniques. But it has also had unwanted effects. For example, the freshwater diversion project disrupted seafood harvesting by coastal communities, and as a result of lawsuits brought against the project, local oystermen have been awarded more than $1 billion in damages.
From 1991 until 1998, more than forty-five projects began under the auspices of the CWPPRA. But it soon became obvious to both state and federal governments that the coastal land loss in Louisiana far exceeded the capabilities of the original CWPPRA legislation to address it. A new effort, known as Coast 2050, was set up to evaluate and plan for a larger-scale restoration of coastal Louisiana. That work resulted in a plan with an anticipated price of $14 billion.
The Coast 2050 effort subsequently evolved into the Louisiana Coastal Area Ecosystem Restoration Project, or LCA, in which I participate as a geologist. In an effort to draft the legislation needed to
The magnitude of the crisis, though, should be obvious: the largest river ecosystem in the United States is collapsing right in front of us. And if leaders are wondering whether we can succeed, the answer is yesour experience with CWPPRA has taught us we can. No handbook for coastal restoration exists, but willing spirits can and will move ahead to restore Americas wetlands.
My colleagues and I proceed according to the best principles of practical science: we apply what we know, we test and adjust in the field, and we are not afraid to seize on unexpected success. But what we learn through hard empirical work will someday create a body of disciplined knowledge that can be applied throughout the world. Our work in Louisiana will someday form part of the foundation of a new fieldenvironmental restoration sciencethat will prove as important to university education in this century as geology and engineering have been to date.
In 1925, one visionary, Percy Viosca Jr. of the Louisiana Department of Conservation, foresaw the impending ecological collapse of coastal Louisiana and the necessity of restoration. He wrote:
Man-made modifications in Louisiana wet lands [are] a failure, destroying valuable natural resources without producing the permanent compensating benefits originally desired. . . . Our future conservation policy should be a restoration of those natural conditions best suited to an abundant marsh, swamp, and aquatic fauna. . . . [With them] the state and nation may enjoy . . . a more enduring prosperity.