The Decatur Dryland Bridge and the “Impetuous” Missouri

In 1946, the Burt County Bridge Commission sought approval from the Army Corps of Engineers to build a bridge over the Missouri River linking Decatur, Nebraska, with Onawa, Iowa. Army officials approved the request with one stipulation – the new bridge had to be built over the yet-to-be-constructed navigation channel, rather than over the existing course of the river, which flowed in a broad, shallow arch 500 feet to the east of the planned bridge.

After receiving the go-ahead, Burt County erected the bridge atop a sandy, dry expanse of Missouri Valley bottomland. When the bridge neared completion in 1951, Burt County officials petitioned the Army to move the Missouri under the bridge. But the Army demurred; it had other priorities along the Missouri. Specifically, Army officials wanted to raise and close Garrison and Fort Randall dams in North and South Dakota before restarting construction on the navigation channel south of Sioux City, Iowa. Officials concluded that closure of those two massive dams would protect the future navigation channel’s pile dikes and revetments from the river’s devastating flood flows, which in the past had wreaked such havoc on the Army’s control works.

For the next four years, the bridge went without a river. The longer the bridge stood silently above the sand dunes, the more attention it received from the media. By the mid-1950s, national media outlets began covering the story of the “Decatur Dryland Bridge” or the “Bridge to Nowhere.” Most of the media coverage portrayed the “Bridge to Nowhere” as an example of Army incompetence, wasteful federal spending, and pork barrel politics.

Finally, in 1955, Congress appropriated $11 million dollars to redirect the Missouri under the $2 million dollar bridge. In late July and early August of that year, the Army diverted the Missouri. It did so by employing an array of sophisticated tools, including a toe-trench revetment, a pile dike revetment, a coffer dam, a pilot canal, a dredge boat, dynamite, hydraulic jacks, and the gigantic earthen dam at Fort Randall. The big dam was instrumental in the diversion of the river under the bridge. Fort Randall cut the flow of the river south of Sioux City from approximately 30,000 cubic feet per second to 3,000 cubic feet per second, or 1/10th its regular flow volume. The trickle of water moving through the Missouri at Decatur enabled the Army to easily nudge the river under the bridge.

The Army’s ability to manipulate the Missouri at Decatur had a profound influence on the thinking of Missouri Valley residents. After the diversion operation, the public viewed the Army with a mixture of awe and fascination; awe at the engineering expertise it displayed at Decatur and fascination at its ability to coordinate so many different technologies during the diversion project. No one doubted that by mid-1955, the Army had achieved a high-level of environmental mastery over the Missouri.

At the same time, the river became diminished in the public’s eye. The Missouri was no longer to be feared. Rather, it was something smaller, more benign, a once mighty stream brought low – literally and figuratively. The “Sioux City Journal” summed up the public’s new perception of the Missouri when it wrote, “…man had at last controlled the impetuous river.”

For 56 years, the Missouri flowed through the Army’s navigation channel beneath the Decatur Bridge. Then, in June 2011, a flood of historical proportions came barreling down the navigation channel. The powerful flood flows punched gaping holes in the Army’s revetments and pile dikes. The Mighty Mo had returned with a vengeance. From Ponca, Nebraska, to Kansas City, Missouri, the resurgent river sliced and diced the navigation channel to pieces.

In 1955, the Army placed a revetment in the river north of the Decatur bridge site. That revetment redirected the Missouri under the bridge and kept the river from entering its former channel area through Tieville Bend. In June 2011, the Missouri blasted through the stone revetment at Tieville Bend and poured its murky waters into its old channel. Once inside Tieville Bend, the river hurried southward, eventually smashing up against Iowa’s Highway 175, which approaches the Decatur Bridge from Onawa. The hard-charging floodwaters tore away at Highway 175 and blew out the sand, gravel and clay that supported the bridge’s east abutment and pillars. The river’s strong currents threatened to dig a new, deep channel to the east of the bridge and directly across Highway 175.

Engineers with the Iowa Department of Transportation became alarmed at the situation at the Decatur Bridge, especially after they learned that the Missouri’s floodwaters had dug a fifty-foot-deep hole near the bridge’s east abutment. If the river succeeded in detaching the bridge from its east abutment, the bridge was doomed. Without the support of its eastern anchor, the bridge’s mid-channel pillars would be unable to withstand the tremendous pressure exerted against them by the river’s high flows. Eventually, the pillars would give out and the bridge would collapse into the river.

To prevent the destruction of the Decatur Bridge, the Iowa DOT rushed men and dump trucks to the scene. Their job – prevent the strong currents that were boring into the riverbed and pushing up against Highway 175 from washing away the east abutment. For days, crews worked around the clock to save the roadway and the bridge. Trucks dumped load upon load of quarried Sioux quartzite into the deep hole and along the edges of the highway. After tons of rock had been placed in the path of the river, the work crews pulled back. There was nothing more they could do. The river was running too high and too fast to attempt additional repairs. In the following weeks, the Iowa DOT’s engineers watched, waited, and hoped that the hastily dumped riprap would keep the Missouri from toppling the Decatur Bridge.

In early October, 2011, the Missouri dipped below flood stage for the first time since May. The DOT’s engineers returned to the Decatur Bridge (which was still standing) to survey the damage to the span and its east abutment. Transportation officials concluded that the bridge and abutment had sustained $3.6 million in damages. They also recognized that the Missouri had come close to destroying the bridge.

The Great Flood of 2011 and the near destruction of the Decatur Bridge fostered a sea change in the thinking of Missouri Valley residents. The river’s unbridled power shattered the once widespread belief, prevalent since 1955, that “…man had at last controlled the impetuous river.”

(Above photograph depicts the Missouri River flowing through the revetment north of the Decatur Bridge into its former channel through Tieville Bend.  Photograph courtesy of Lee Valley, Incorporated, Tekameh, Nebraska.)

This entry was posted in Featured, From the Flood Zone, Missouri River Flood 2011 and tagged , , , , , , , , , , . Bookmark the permalink.

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