Somewhere along the line it was decided that it was the Mississippi River that flowed from Lake Itaska to the Gulf of Mexico and that the Missouri River flowed from the Rockies into the Mississippi. Why couldn’t it have been the Missouri that flowed all the way to the Gulf and the Mississippi that flowed into the Missouri?
And instead of the Allegheny and Monongahela coming together to form the Ohio, why couldn’t what we call the Ohio have been just a continuation of one of the other two streams?
OK, in some cases it’s obvious when a tiny creek enters a large river. But in cases similar to whatI mentioned, it isn’t always so obvious. What rules do geographers use to determine what is tributary and what is the main stream?
My understanding is that general modern practice is to designate the branch that travels the farthest as the “main” river. I don’t remember where I got that. However, all historical anomalies are grandfathered in, which accounts for the Mississippi and the Ohio.
If I recall, it was believed that the Mississippi originated somewhere deep in what is now Canadian territory.
Also, I seem to recall that when the Ohio valley was claimed by France, their maps showed the Allegheny continuing on from Fort Duquesne.
According to Isaac Asimov, at the time the junction of the Mississippi and Missouri was discovered little was known about the Missouri. The Missippi was well known to be a great river whereas it was possible that the Missouri was just a short stream that came in just above St. Louis so it was regarded as the tributary.
It might also have something to do with the volume of water. The Missouri flows through some pretty arid country for much of its length and so doesn’t have as great a flow as the Missippi at their junction. The Mississippi watershed at the junction of the two is nearly as large as that of the Missouri and is much wetter. It extends up the Ohio all of the way into New York state and this adds tremendously to the MIssissippi flow which is already big at Alton, IL.
Another anomaly like the Mississippi-Missouri river system is the Murray-Darling system in Australia, where the Darling River system goes further back from the confluence than the Murray does. And I say “Darling River system”, because the Darling River is not as long as it might be (in much the same way as the Ohio River is not as long as it might be): to get the maximum length out of the system you might add the Barwon River, then to that the Dumaresq River (both of which form part of the boundary between New South Wales and Queensland).
Personally, I think that the mis-labelling of the Missourissippi River was purely political. The Louisiana Territory, which France claimed, was all of the land drained through New Orleans, on the right side of the Mississippi River. The left side of the river was transferred to other countries (England, at the time, I think). If they had defined the river in the logical way, they would have ended up giving a huge chunk of the Plains and West to England, but defining it the way they did, they kept all of that.
I couldn’t see how this is even remotely possible unless you accept that the English (and possibly the French too) were complete idiots. If the English had actually wanted France to concede the territory between the Mississippi and the Missouri, do you think that the name issue would have stopped them from trying to get at it? And, vice-versa, if you believe that the French did not want to give up that territory, would they purposely used a designation that was intentionally ambiguous?
I mean, how do you see that conversation going?
French ambassador: We propose to draw the border at the Mississippi River.
English ambassador: We agree.
French ambassador: Oh, and we have another, completely unrelated matter to discuss.
English ambassador: Righto.
French ambassador: We propose that this branch here be designated the Riviere Mississippi.
English ambassador: Sounds good. Okay.
Frenchman snickers and twirls his moustache.
English ambassador: What? What’s so funny?
French ambassador: See what you’ve done? You’ve just agreed that this is the Mississippi, but before you said the Mississippi would be the border! Hah! That means you get only half of what you wanted!
English ambassador: Damn and blast!
French ambassador: No take backs!
English ambassador: It’s a fair cop.
Not so. La Salle initially claimed the entire Mississippi watershed (including the Missouri and Ohio) for France in 1682. All these territories were lost at the end of the French and Indian War (Seven Year’s War) in 1763, those east of the Mississippi going to Great Britain and those to the west to Spain.
France temporarily regained the territory to the west of the Mississippi from Spain during the Napoleonic Wars, but sold them to the US as the Louisiana Purchase.
I may be misunderstanding your intent, here, but I will point out that at the point where the Missouri and Mississippi converge, the Ohio is still many miles downstream. The water in the Mississippi at the point of confluence does not include anything from the Ohio/Tennessee/Alleghany/Monongahela system.
On the other hand, the general point of flow volume is legitimate. Despite its shorter length (and despite not yet having been augmented by the Ohio), the Mississippi flow at the confluence is quite a bit greater than the Missouri flow.
The argument from “flow” is hardly conclusive, of course. There is no strictly logical reason why either the Alleghany or the Monongahela could not be the Ohio. (Or, for that matter, why the Jefferson, the Madison, or the Gallatin could not be the “real” Missouri intead of having three rivers combine to “become” the Missouri.)
I always suspected that in cases such as the Ohio, European explorers from the West applied the local name for the Ohio while explorers coming from the East applied local names to the Alleghany and Monongahela and they simply determined that where they met, each river kept its own name. On the other hand, it is possible that the indigenous nations had already used the tripartite name scheme and the white settlers simply continued to use it. (No such answer is possible for the Missouri, of course, meaning that Lewis and Clark had to botch that up, themselves.)
“…in an average year, the Missouri River provides about 45 percent of the flow of the Mississippi past St. Louis. Its volume on average is also less than that of the Ohio River, another tributary of the Mississippi”
In my neck of the woods (literally), the Bow and Oldman river join and become the South Saskatchewan. The North Saskatchewan and South Saskatchewan join and become the Saskatchewan.