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Only in Arkansas: Marked Tree Siphons lift a river

The Marked Tree Siphons installation, dating to 1939, is said to be the only engineering structure of its kind in the United States.
The Marked Tree Siphons installation, dating to 1939, is said to be the only engineering structure of its kind in the United States.

Among the most frequently misused words in the English language is "unique." It means "one of a kind," not just "quite unusual." To describe anything as "somewhat unique" is as misbegotten as saying that a woman is "somewhat pregnant."

But there are truly "unique" objects and situations. One example worth a stop when traveling in northeast Arkansas is the Marked Tree Siphons. This one-of-a-kind construction can be viewed about seven miles north of Marked Tree, the Poinsett County seat in Sunken Lands terrain that shifted and fell during the 1811-1812 New Madrid earthquakes. It was listed on the National Register of Historic Places in 1988.

Built in 1939 by the U.S. Army Corps of Engineers, the three massive tubes are described by the Encyclopedia of Arkansas History & Culture as "an integral part of the St. Francis Basin Flood Control Project. The siphons were also a unique application of an engineering structure of their type, designed to lift the flow of the St. Francis River over an earthen levee and deposit it in the river channel on the other side of the levee."

In this instance "unique" fills the bill, for there is evidently no similar structure elsewhere in the United States -- and quite possibly elsewhere in the world. How the project was built, after previous engineering attempts failed, makes for a fascinating story in the longstanding efforts to control flooding in the Arkansas Delta.

Back in 1926, a floodway plus lock and sluiceway were completed as part of plans to tame the St. Francis by diverting overflow during high-water periods. But 40 feet of the sluiceway broke in 1933, leading to partial collapse of the levee. After Corps of Engineers repairs, the sluiceway was damaged again in 1938, this time beyond repair. The collapses evidently happened because the fine-grained soil below would turn to quicksand when saturated.

That led to the unparalleled design of the siphons. At the dedication ceremony on June 8, 1939, the project was christened with a bottle of champagne. A correspondent for the Marked Tree Tribune reported that "a whole river was lifted 30 feet across a dam and deposited on the other side."

Built at a cost of $215,000, the three steel tubes integral to the design were among the largest in the world, with diameters of nine feet and lengths of 228 feet. As described by the Arkansas encyclopedia, "Their operation was deceptively simple. First, a vacuum pump primed each siphon. Once the siphon was primed, the vacuum pump was turned off, and the flow was self-sustaining. An air valve regulated the rate of flow."

Once activated, the siphons can run indefinitely, powered only by gravity. Eight decades later, the pumping process still functions properly after an overhaul in the 1990s. As the Arkansas encyclopedia notes, the siphons "have maintained the St. Francis River in its natural channel, as well as protecting agricultural resources and permitting expanded settlement in the area. Tests of the completed siphons revealed an operating efficiency of 97.1 percent."

Visitors to the National Register site can look over the siphons from a small bridge built over the tubes after the gates of the adjoining lock were removed. There is likely to be nobody else present, leaving the imagination free to divine that these mysterious devices might have landed from some science-fiction movie.

To reach Marked Tree Siphons, take U.S. 63 for about two miles west from the town of Marked Tree. Then turn right on unpaved and dusty Lock and Dam Road, continuing 5 miles to the National Register site. Information on the siphons is available at Marked Tree Delta Area Museum, 308 Frisco St. Visit markedtreechamber.org/City%20Museum.htm or call (870) 358-4998.

Weekend on 06/21/2018

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