What do you call a small river that branches off from a bigger one?
A stream, creek, run, or river; I’m not sure that there is such a thing as a “reverse tributary.”
Except in the cases of a river delta or to go around an island, rivers rarely split into two streams. Because of that, there’s no real need for a special term for the phenomenon.
The closest that I can think of is anabranch, the term for a river channel that splits off the main trunk but that rejoins it at some later point. As dtilque points out, it’s almost unheard of (well I’ve never heard of it) for a stream to leave a river and never rejoin it. It could really only possibly occur if a mountain or similar cause the river to split very close to the coast so that the there were two river mouths produced.
Back in school, we learned in geometry that a small river branching off from a bigger one is a distributary. Cite.
Ya that’s right…my geometry teacher loved teaching us topography. :smack:
Distributaries, and they are almost always associated with deltas.
If there was a word, I knew the Teeming Millions would know it. 
Distributary. Awesome.
There is at least one river that splits without rejoining: the Orinoco in South America. The main channel goes north to the Caribbean while part of it goes south and ultimately drains into the Atlantic via the Amazon. This may be a unique case in the entire world.
Nope, not unique: what you’ve just described is a distributary on the Orinoco Delta. Although it is pretty cool that one distributary drains into the Carribean and the rest drain into the Atlantic, it is just a delta distributary.
Here’s a map of Venezuela that shows the Orinoco Delta. And you can click on this map of the Orinoco Delta to see a better close-up view.
In the Canadian Rockies, on the border between BC and Alberta, there’s a creek that splits into two creeks. One flows west to the Pacific, while the other flows east to reach Hudson Bay. The location of the split is pretty far from both oceans.
Cite (scroll down to the paragraph on the Continental Divide.)
The delta doesn’t enter into it. The bifurcation is much more upstream, where the Casiquiare canal branches off to join the Rio Negro and eventually tha Amazon river. Here’s a much better map.
Thanks, Floater! Very odd. Maybe it is unique after all.
The Pearl River in southern Mississippi also splits into two distributaries: the east fork and the west fork.
The Rhine River splits into three or more pieces through Holland and Belgium. Of course you could say that the whole area is the Rhine delta, but that’s a pretty large area.
That is fascinating, but why is it called a “canal”? Wikipedia refers to it as a “natural canal”, which is oxymoronic. From the AHD, a canal is:
Bolding mine. The feature is natural, and from the description of it, pretty much non-navigable.
It could be that the name is straight from the Spanish. “Canal” can mean channel in addition to canal.
So then that would be the “Orinoco Flow”?
Any Enya fans?
Although it’s probably smaller than the Amazon delta. But then the Amazon has many times the flow of the Rhine, so I guess that’s to be expected.
From what I understand, about 30% or so of the Mississippi River flows out the Atchafalaya River. In fact, if it weren’t for heroic efforts by the Army Corp of Engineers, the Atchafalaya would now be the main channel.
Read John McPhee’s The Control Of Nature for an excellent history of that occurence.