KANSAS CITY, Mo. » The meandering path of the Missouri River, charted by Lewis and Clark, once served as the main travel artery across the Great Plains, carrying people and goods between the comforts of St. Louis and the wilds of the Montana territory.

But as railroads and highways replaced the river as the preferred shipping routes, barge traffic dried up so much that some ports have gone years without seeing a single one. And now the river is dividing the region that it had stitched together with each of its oxbow bends.

The record flooding this summer along the Missouri River has overwhelmed dams and levees, swamped small communities and forced large cities into emergency measures to hold the water back. And so the pressing matter of how to manage flooding on the Missouri has added a new urgency to the contentious question that has long nagged this region: What precisely is this river for?

In a normal year, the water that is used to keep the river level high enough for barges comes from releases from the dam system built to control river flow. But the states north of the dams, including North and South Dakota, have argued that the river is no longer needed for navigation and that more water should be kept in the reservoirs for recreation, to help the region’s economy.

The summer-long flood brought promises of renewed cooperation after years of legal and legislative battles. Sen. Claire McCaskill, D-Mo., said a recent meeting of a group of senators to examine how the waterway was managed represented "a high point, pardon the expression, for cooperation for states along the Missouri River."

But these leaders have not yet breached the underlying concerns about how the federal government manages the water.

Earlier this year, the Missouri congressional delegation succeeded in stripping financing, after more than $7 million had been spent, from a study of the priorities for river management that was supported by upriver states, arguing that it was redundant and amounted to an attack on navigation.

Even as McCaskill praised the collaboration in fighting flooding, she noted that she and other leaders from both parties in Missouri remained committed to supporting shipping interests on the river. "While navigation is much more important than recreation, we should not let the fight between navigation and recreation get in the way of flood control," McCaskill said.

Her colleagues north of the dams have a different view.

"Frankly, navigation never developed as anticipated," said Sen. Kent Conrad, D-N.D., who called for a revision of how the river was operated. "The basic operational assumptions from the management of the river are really no longer valid."

Asked about the continued emphasis on navigation despite the sparse traffic, Jody Farhat, chief of water management for the Missouri River Basin for the Army Corps of Engineers, said: "The primary reason is it’s because it’s the law. The Corps of Engineers does what Congress tells us to do."

Once wide, shallow and unusually winding, the Missouri River has been drastically reshaped over the last century, at a cost of more than $650 million, to create a channel friendly to modern vessels, according to federal estimates. The result is a narrower, deeper, straighter river, which the government spends about $7 million a year to maintain.

The predictions for boat traffic that were used to justify the spending never materialized. The amount and value of river freight has actually declined sharply since the late 1970s, a few years before the project was finally completed, according to federal data.

Though the river cuts through the heart of farm country, almost no grain is transported on the Missouri — 4.8 million of the 5 million tons of cargo moved by barge last year was sand and gravel, which was usually shipped less than a mile. Traffic upriver from Kansas City all but disappeared.

Other rivers have shown that shipping can still be viable. Though slower than other forms of transit, river barges are able to carry far larger quantities at a lower cost. Even with aging infrastructure on many major shipping routes — and despite the widespread flooding this year — the business as a whole remains healthy, industry leaders say.

But the Missouri can accommodate fewer barges because of the strong current and sharper bends. And though navigation, along with flood control, gets priority for releases of water from dams, the unpredictable river levels have made shipping contracts riskier.

The most substantial contribution to navigation that the river makes is supplying water to the far busier Mississippi, into which the Missouri empties just north of St. Louis.

Officials with the Army Corps of Engineers have said that the reservoir levels were drawn down to "full flood capacity," when rain unexpectedly filled the space set aside for snowmelt — forcing the dams to release more water than ever before. Various parties have suggested that more water than necessary was being held back. Corps leaders acknowledge the tension between vacating water for a flood and holding it for other use, but maintain that the guidelines never anticipated a flood of this size.

That defense has not assuaged Gov. Terry E. Branstad of Iowa, a Republican, who has strongly criticized the Corps of Engineers for not releasing more water sooner. He said he believed that the other uses, like navigation and recreation, distracted from the focus on flood control.

"They’ve lost their way," Branstad said. "They’re not doing what the dams were designed to do in the first place. As a result, we’ve suffered significant losses."

© 2011 The New York Times Company