First, they did not necessarily head back up the river. Flatboats and bateaus ( or bateaux, if you want to stay loyal to French) were commonly knocked-together craft that would be steered downstream. The cargo would be sold, and then the boat itself would be sold for lumber. The crew would then walk home ( a very common use for the Natchez Trace).

But there would be keelboats as well, typically better made, which could get unloaded and be ready for another trip. They might be loaded with another cargo: a boatload of barrel staves might be unloaded in New Orleans, and a variety of trade goods, like calico cloth and copper kettles, hauled back upstream. Getting that upstream was, however not easy. One possibility was for the crew to pole the boat. Depending on the current, that could be an easy task or a very difficult one. But it was easier than "cordelling", letting out a long towrope and having the crew haul it upstream. That was necessary when the current was too fast and the bottom too insecure for poles. That's what is happening in this drawing, though here the crew has a nice river bank to work from, without trees and brush. When Lewis and Clark went west, the crew did a lot of cordelling wading in the river, and it was very hard going.

Note the poles hanging on the rack on the side of the cabin, ready to be deployed.

Some rivers would be wide and straight enough for a sailboat. The Hudson River had merchant ships, now called Hudson River sloops, that took advantage of the fact that the Hudson Valley had quite steep sides that made coach and wagon roads difficult, so there was less competition from land traffic. That would also be a key reason why the Hudson was lucrative for Robert Fulton's North River Steamboat in 1809, when it appeared.

There were rivers that were simply impractical, however. The Potomac , with its many ledges, rapids and rocky shoals, was barely passable to downstream traffic when the water was high enough. George Washington and a company of investors formed the Potowmack Company in 1785 to cut through obstacles and build a few locks to make traffic possible. They hired James Rumsey as a superintendent, partially because he was going to develop a self-powered boat of his invention that would ascend against the current. He had two propulsion methods: one was to have a paddlewheel work some poles, pulling the boat somewhat like a cross-country skier pushes herself on skies, the other used a steam engine to pump water out the stern, like a modern jet boat. The paddle-wheel powered poles had problems with stability ( when the boat wasn't pointing directly upstream, the paddlewheel stopped working).The steam-powewred jet boat worked better, but brought him into conflict with John Fitch's steamboat project in Philadelphia, and both ultimately failed. Rumsey kept toying with the idea of the paddle-wheel powered poleboat, took out a patent on an improved version when he moved to England. But he never built another.

On the Mississippi and its tributaries, flatboats went downstream, while faster, deeper-draft keelboats went both ways. Davy Crockett’s memoir, though it must be taken with a substantial grain of salt, contains fine accounts of river travel, including a wonderful anecdote about a flatboat sinking. And as Mark Twain knew well, folks who could do no better could and would set out on a raft. General histories mention these methods, but travelogues and memoirs are more helpful for getting a sense of how they worked and what they felt like.

Keels could be towed or rowed, but flats were too broad and unwieldy to pull against current. They could be sold as floating homes or broken up for lumber at the mouth of the Mississippi, while their crews hired on as keeler crew or joined land-based caravans to return north.

The following books have rich descriptions of these modes of travel:

Baldwin, L. D. The Keelboat Age on Western Waters. Pittsburgh: University of Pittsburgh Press, 1941

Crockett, David. A Narrative of the Life of David Crockett. Baltimore, MD: E. L. Carey and A. Hart, 1834.

Russell, Charles Edward. A-Rafting on the Mississippi. New York: Century Co., 1928.