Could today's flooding of the Mississippi have been prevented?

::::::::

PETER'S NEW YORK, May 10, 2011--As the Mississippi rises to well above flood stage, resulting in hundreds of millions of dollars of property damage, it might do well to re-examine the proposal of a 19th Century civil engineer to tame the river's waters.

George Holt Henshaw by P. Duveen

George Holt Henshaw had been preoccupied with the problem of periodic flooding of the Mississippi River at least since 1881, when he submitted a paper in a competition sponsored by the King of Belgium on the improvement of harbors on sandy coasts. As an engineer involved in the construction of canals and other water works, he had studied water flow and erosion, and wished to apply his expertise to a vexing dilemma: how to keep the Mississippi navigable while protecting the population that had permanently settled in what was formerly the flood plain of the river. Since the river overflowed only periodically, and severe flooding was even less frequent, the population had seen fit to establish permanent residences and farms in the countryside surrounding the river, and to erect and maintain mounds of earth at the banks of the river in order to prevent the river's waters from flowing into settled areas. These reinforced mounds of earth are what are generally referred to as levées.

Henshaw believed that the levée system was doomed to failure, because it concentrated in the artificially narrowed river channel the deposit of sediment that would otherwise have been spread across the broad stretches of the river's natural flood plain. This sediment would eventually displace a significant volume of water, which would have no place to go but over the levées. The cycle of failure, according to Henshaw, would persist even as the levées were built higher and stronger in an attempt to protect residents from the river's overflow.

Henshaw believed he had a solution. When he was involved in railway construction in Canada and Denmark, he had observed the manner in which snow banks were formed and shaped by the wind. Small obstacles to the wind created either a buildup of snow, or deep furrows within snow banks, depending on where they were situated. This shaping of the accumulated snow by the wind occurred according to strict natural laws, and Henshaw believed that these same laws applied to the manner in which the silty riverbed reacted to the flow of water.

In 1882, Henshaw addressed the problem of Mississippi flooding in a paper, "A Plan for the Improvement of Navigation and the Prevention of Floods in the Mississippi River." At that time, it had been argued that by narrowing the banks of the river, the water could be induced to flow more rapidly, and would be more apt to carry away sediment. But Henshaw countered that it was not velocity alone, but also turbulence, that determined whether sediment was carried away. This turbulence, if artificially maintained, might result in the natural deepening of the river channel through the carrying away of sediment.

Some success had already been achieved in deepening parts of the Mississippi without resorting to dredging or levées. James Buchanan Eads (1820-1887) had managed to fulfill a contract around 1879 to deepen a heavily trafficked portion of the Mississippi delta known as the South Pass, by the construction of jetties into the river. He was successfully able to maintain a depth of 30 feet, and his accomplishment was widely acclaimed. But the Army Corps of Engineers, which had the upper hand in crafting policies relating to the river, eventually dropped Eads's successful innovations and soon moved to a plan focusing on levée construction and repair.

Channel of the South Pass, Mississippi Delta, 1874 map. by Museum of Brooklyn Art and Culture

In a second paper on the subject, published in March of 1889 in the Journal of the American Society of Civil Engineers, Henshaw argued for the strategic placement on the river bed of fences composed of willow branches. These seemingly innocuous obstacles, he believed, would generate the turbulence required to deepen the river.

In 1890, Henshaw was awarded a patent for an invention "by which river channels may be formed and preserved, bars off the mouths of deltas removed and the channels through deltas deepened and preserved, sea beaches repaired and protected from erosion, shifting shoals fixed, and estuary lands reclaimed."

Illustrations of Henshaw's scheme to deepen river channels. by Museum of Brooklyn Art and Culture

Henshaw appealed to the Mississippi River Commission, established by the U.S. Congress in 1879 to manage the flooding of the river, but was unable to evoke a positive response. A new and devastating flood in 1890 demonstrated that the best efforts of the commission were not bearing fruit, despite the tens of millions of dollars applied to the commission's various projects at different points on the river. The renewed flooding prompted Henshaw to appeal to the public in a letter to The New York Times.

Henshaw's plan would have narrowed and deepened the channels of rivers. by Museum of Brooklyn Art and Culture

"No one now disputes," said Henshaw," that the Mississippi runs through an elevation which it has itself deposited, nor that this deposit still goes on. This being the case, it is plain that the deposit, which in ancient times spread itself far and wide, is now confined between the levées; therefore, unless the channel or channels be made to deepen and widen themselves in proportion to the deposit, the bottom must rise, and the height of the levées must be increased from time to time."

The commission, Henshaw suggested, had failed to prevent renewed flooding of the river because "more deposit has taken place than scour, for otherwise the flood would not have risen to so great a height." Henshaw never was able to see his letter in print, for, as The Times noted, "the above communication was brought to The Times office by Mr. Henshaw three days before his death."

One can't help but wonder what the Mississippi Valley would look like today if Henshaw's recommendations had been heeded. Certainly, the disaster that is taking shape before our very eyes would not have occurred. Is it time to reconsider the way in which we relate to the natural forces that shape our everyday lives, forces that could be used to our benefit if we merely adopted the right strategy.

(The above article is a reworking of an earlier version that was published on OpEdNews.)