Far Outliers

A LEVEE IS NOTHING MORE than earth mounded into a hill to contain water. Babylonians leveed the Euphrates. Rome leveed the Tiber and Po. By 1700 the Danube, the Rhone, the Rhine, the Volga, and other European rivers had levees, while Holland made the most extensive use of them (a levee and a dike are the same thing).

The Mississippi creates natural levees. When the river overflows, it deposits the heaviest sediment first, thus building up the land closest to the river. Generally, these natural levees extend for half a mile to a mile from the riverbank. “Bottomlands” farther away are lower and often marsh and swamp. New Orleans was founded on a natural levee, and its French Quarter is the highest ground in the region. By 1726, artificial levees with a height ranging from four to six feet also protected the city.

But levee building never stopped; levees were extended above and below New Orleans, then to the opposite bank. Those levees increased the pressure on old ones. The reason is simple: when the river was leveed on only one bank, in flood it simply overflowed the opposite bank. But with both banks leveed, the river could not spread out. Therefore, it rose up. Thus the levees, by holding the water in, forced the river higher. In turn, men tried to contain the flood height by building levees still higher. By 1812, levees in Louisiana began just below New Orleans and extended 155 miles north on the east bank of the river and 180 miles on the west bank. By 1858, levees on the two sides of the river totaled well over 1,000 miles.

In some stretches the levee rose to a height of 38 feet. These heights changed the equations of force along the river. Without levees, even a great flood—a great “high water”—meant only a gradual and gentle rising and spreading of water. But if a levee towering as high as a four-story building gave way, the river could explode upon the land with the power and suddenness of a dam bursting.

From the first, some critics argued that building the levees higher simply increased the dangers should a crevasse, or levee break, occur, and insisted that a means to lower flood heights be used in conjunction with levees. There were three main ways to lower the flood level. One was to build reservoirs on tributaries to withhold water from the Mississippi during floods. A second was to cut a line through the sharp S curves of the river; these cutoffs would move the water in a shorter and straighter line, increase its slope, and hence its speed (a book arguing for cutoffs would later be titled Speeding Floods to the Sea). A third way was to let water escape from the river through outlets. All three proposals had detractors, but outlets had the most—because it also had the most advocates.

As early as 1816, proposals were made to create artificial outlets, also called spillways or waste weirs, on the east bank of the Mississippi near New Orleans. One proposal called for a spillway above the city to drain Mississippi floodwater into Lake Pontchartrain, while another called for one below the city to drain into Lake Borgne. Both “lakes” are really more akin to saltwater bays and empty into the sea, and at the proposed sites the river flowed within five miles of them.

Simple logic drove the argument for outlets. Removing water from the river would lower flood levels, proponents of the scheme insisted, just as removing the plug in a bathtub lowered the water level there.

Critics of outlets who instead insisted upon levees, and levees only—it soon became known as the “levees-only” position—generally subscribed to an engineering theory developed from observations of the Po made by the seventeenth-century Italian engineer Guglielmini. Guglielmini argued that alluvial rivers, like the Mississippi, always carried the maximum amount of sediment possible, and that the faster the current, the more sediment the river had to carry. His hypothesis further argued that increasing the volume of water in the river also increased the velocity of the current, thus compelling the river to pick up more sediment. The main source for this sediment had to be the riverbed, so confining the river and increasing the current forced a scouring and deepening of the bottom. In effect, adherents of this theory argued, levees would transform the river into a machine that dredges its own bottom, thus allowing it to carry more water without overflowing.

Levees-only advocates argued that outlets, by allowing water to escape from the river, were counterproductive since they removed volume from the river, lowered the slope, and caused the current velocity to slow. This not only prevented the current from scouring out the bottom, but actually caused the deposit of sediment—thus raising the bottom and in turn the flood height. According to the levees-only theory, using outlets was like taking water out of a bathtub, then dumping so much gravel into it that the tub ended up holding less water. The levees-only hypothesis argued that outlets, rather than lowering the flood height, would actually raise it.

SOURCE: Rising Tide: The Great Mississippi Flood of 1927 and How It Changed America, by John M. Barry (Touchstone, 1998), pp. 40-41 (reviewed here)

Nicole Gelinas, writing in the 28 August 2006 issue of City Journal, says the Katrina flooding was, above all, a failure of engineering and infrastructure.

Katrina was the biggest test of the 350 miles of levees and floodwalls that the Corps built and refurbished over the past 40 years–and the system crashed, buckling under 50 major breaks and spilling millions of gallons of water into the city. And Katrina was far from a worst-case scenario.

The Corps’ post-mortem of Katrina tells the story: “the system did not perform as a system,” its engineers concluded. “The hurricane protection in New Orleans … was a system in name only…. The majority, approximately two-thirds by volume, of the flooding and half of the economic losses can be attributed to water flowing through breaches in floodwalls and levees.” The failures weren’t due to construction malfeasance or incompetence: “the system was built as designed,” the Corps concluded. But the system was, in many ways, conceived to fail. In the Corps’ view, it was inconsistently designed and lacked redundancy–that is, back-up protections.

Some levees, in particular the massive earthen fortresses with wide foundations, performed well, withstanding days of water pressure with little erosion. But floodwalls designed as narrow vertical walls driven into the ground–they look like the walls built on highways to block out the noise–performed abysmally.

First, some walls had sunk up to three feet lower than their original “authorized heights” before the storm. Second, the pressure of Katrina’s waters wore away the walls’ narrow vertical foundations because they weren’t “armored” with erosion-proof material, causing the structures to topple into the water. And because the system wasn’t redundant, each break caused additional weaknesses.

Why didn’t the Corps design a consistent, redundant system? In large part, the reason was foot dragging–or worse–by pols on the state, local, and federal levels. In some cases, political opposition prevented the Corps from seizing land to build sturdier foundations. Plus, Louisiana’s local levee boards were lousy stewards. Levee officials were political animals, not engineering experts, and sometimes proved more interested in running ancillary “economic development” projects than working with the Corps to make sure the levees were up to their task. (It’s not because New Orleans is poor and black: the levees protect New Orleans’s richer, whiter suburbs too.) In addition, the Corps warned that many of New Orleans’s manmade canals, obsolete for years, should be closed or at least gated–to no avail. Moreover, when the Corps, along with state officials, came to understand that wetlands restoration is a vital part of the flood protection system, not a tree-hugger’s afterthought, Congress balked at spending the required $14 billion over several decades for coastal restoration….

President Bush’s recent rhetoric thus doesn’t help New Orleans or the nation. He still talks as if poverty, and not inadequate design and investment in the plain, old, boring infrastructure that makes all cities work, was responsible for Katrina’s tragic devastation.

UPDATE: Nathanael of the always insightful Rhine River blog asks:

One question scholars have yet to answer: why can’t cities, as they did in the past, undertake the grand construction projects of this type? Is there something about the nature of the challenge, be it financial, legal, engineering, …, that not only makes the federal government better at these projects, but the only actor that can undertake them?

To shed a bit of light on this question, here’s a quote from John M. Barry’s Rising Tide, which I’ve been reading and excerpting:

For decades the increasingly populated states of the Mississippi valley had been demanding that the national government address navigation and flood problems on the Mississippi River. Conventions in Cincinnati in 1842, in Memphis in 1844, in Chicago in 1847 (where 16,000 delegates overwhelmed a city of 10,000) had pressured Washington to act. At last, to keep the West, the upper Mississippi valley, from forging a political alliance with the South and spurred on by a flood in 1849 that inundated much of the lower Mississippi valley—including New Orleans itself—eastern politicians acceded to the demands, and Congress ceded millions of acres of federally owned “swamp and overflowed lands” to the states. (Footnote: Louisiana received 9.5 million acres, Arkansas 7.7 million, Missouri 3.4 million, and Mississippi 3.3 million.) The states were to sell the land and spend the proceeds on flood control.

When states fall down on the job, as they did in 1927 (and 2005), the Feds are the saviors of last resort. (In failed states, international institutions are the saviors of last resort.)